### Example of anyhow::Result in main

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

This example shows how anyhow::Result can be used in the main function. Failures will be printed with context and a backtrace if captured.

```rust
use anyhow::Result;

fn main() -> Result<()> {
    let config = std::fs::read_to_string("cluster.json")?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    println!("cluster info: {:#?}", map);
    Ok(())
}
```

--------------------------------

### Example Usage of anyhow::Result

Source: https://docs.rs/anyhow/latest/src/anyhow/lib.rs.html

An example demonstrating how `anyhow::Result` can be used in a function that might return a deserialized JSON value or an I/O error.

```rust
# pub trait Deserialize {}
# 
# mod serde_json {
#     use super::Deserialize;
#     use std::io;
# 
#     pub fn from_str<T: Deserialize>(json: &str) -> io::Result<T> {
#         unimplemented!()
#     }
# }
# 
# #[derive(Debug)]
# struct ClusterMap;
# 
# impl Deserialize for ClusterMap {}
# 
use anyhow::Result;

```

--------------------------------

### Example Usage

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Demonstrates how to use the `chain` iterator to find a specific underlying error type.

```APIDOC
## §Example
```rust
use anyhow::Error;
use std::io;

pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
    for cause in error.chain() {
        if let Some(io_error) = cause.downcast_ref::<io::Error>() {
            return Some(io_error.kind());
        }
    }
    None
}
```
```

--------------------------------

### Example of Adding Context to a Parse Error

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Demonstrates how to use anyhow::Error::context to add specific information to a custom error type during error propagation. This example shows how to include the line number and file path in the error context.

```rust
pub fn parse(path: impl AsRef<Path>) -> Result<T>
    {
        let file = File::open(&path)?;
        parse_impl(file).map_err(|error| {
            let context = format!(
                "only the first {} lines of {} are valid",
                error.line, path.as_ref().display(),
            );
            anyhow::Error::new(error).context(context)
        })
    }
```

--------------------------------

### Example Usage of Context

Source: https://docs.rs/anyhow/latest/src/anyhow/context.rs.html

Demonstrates how to use the `context` method on an `Option` to provide an error message if the option is `None`. This is a common pattern for handling potentially missing values.

```rust
# type T = ();
#
use anyhow::{Context, Result};

fn maybe_get() -> Option<T> {
    # const IGNORE: &str = stringify! {
    ...
    # };
    # unimplemented!()
}

fn demo() -> Result<()> {
    let t = maybe_get().context("there is no T")?;
    # const IGNORE: &str = stringify! {
    ...
    # };
    # unimplemented!()
}
```

--------------------------------

### Example Usage of Context

Source: https://docs.rs/anyhow/latest/anyhow/trait.Context.html

Demonstrates how to use the `context` and `with_context` methods to add human-readable context to errors, improving debugging by providing more information about the error's origin and circumstances.

```APIDOC
## Example
```rust
use anyhow::{Context, Result};
use std::fs;
use std::path::PathBuf;

pub struct ImportantThing {
    path: PathBuf,
}

impl ImportantThing {
    pub fn detach(&mut self) -> Result<()> { /* ... */ }
}

pub fn do_it(mut it: ImportantThing) -> Result<Vec<u8>> {
    it.detach().context("Failed to detach the important thing")?;

    let path = &it.path;
    let content = fs::read(path)
        .with_context(|| format!("Failed to read instrs from {}", path.display()))?;

    Ok(content)
}
```

When printed, the outermost context would be printed first and the lower level underlying causes would be enumerated below.
```
Error: Failed to read instrs from ./path/to/instrs.json

Caused by:
    No such file or directory (os error 2)
```
```

--------------------------------

### Chain::new

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Constructs a new Chain iterator starting with the given head error.

```APIDOC
## pub fn new(head: &'a (dyn StdError + 'static)) -> Self

Constructs a new Chain iterator starting with the given head error.
```

--------------------------------

### Type Inference Error Example

Source: https://docs.rs/anyhow/latest/anyhow/fn.Ok.html

This example demonstrates a scenario where type annotations are needed because the compiler cannot infer the error type `E` for `std::result::Result` when using `anyhow::Result::Ok` directly.

```rust
error[E0282]: type annotations needed for `std::result::Result<i32, E>`
  --> src/main.rs:11:13
   |
11 |     let _ = anyhow::Result::Ok(1);
   |         -   ^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `E` declared on the enum `Result`
   |         |
   |         consider giving this pattern the explicit type `std::result::Result<i32, E>`, where the type parameter `E` is specified
```

--------------------------------

### Chain::new

Source: https://docs.rs/anyhow/latest/src/anyhow/chain.rs.html

Constructs a new Chain starting with the given head error. This is the entry point for iterating over an error's source chain.

```APIDOC
## Chain::new

### Description
Constructs a new `Chain` starting with the given head error.

### Method
`new`

### Parameters
#### Path Parameters
- **head** (`&'a (dyn StdError + 'static)`) - Required - The starting error in the chain.
```

--------------------------------

### Example: Using Error::msg in Stream Combinators

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Demonstrates how `Error::msg` can be used with stream combinators to convert errors from operations within the stream into anyhow::Error objects.

```rust
async fn demo<S>(stream: S) -> Result<Vec<Output>>
where
    S: Stream<Item = Input>,
{
    stream
        .then(ffi::do_some_work) // returns Result<Output, &str>
        .map_err(Error::msg)
        .try_collect()
        .await
}
```

--------------------------------

### Handling File Metadata with Result

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Demonstrates using `and_then` to chain fallible operations like getting file metadata and its modification time. Errors are checked using `is_ok` and `is_err`.

```rust
use std::{io::ErrorKind, path::Path};

// Note: on Windows "/" maps to "C:\\"
let root_modified_time = Path::new("/").metadata().and_then(|md| md.modified());
assert!(root_modified_time.is_ok());

let should_fail = Path::new("/bad/path").metadata().and_then(|md| md.modified());
assert!(should_fail.is_err());
assert_eq!(should_fail.unwrap_err().kind(), ErrorKind::NotFound);
```

--------------------------------

### Adding Context to Results

Source: https://docs.rs/anyhow/latest/anyhow/trait.Context.html

Demonstrates how to use the `context` and `with_context` methods to add human-readable context to errors. The `context` method adds immediate context, while `with_context` evaluates the context lazily. This example also shows how context is displayed when an error is printed.

```rust
use anyhow::{Context, Result};
use std::fs;
use std::path::PathBuf;

pub struct ImportantThing {
    path: PathBuf,
}

impl ImportantThing {
    pub fn detach(&mut self) -> Result<()> {...}
}

pub fn do_it(mut it: ImportantThing) -> Result<Vec<u8>> {
    it.detach().context("Failed to detach the important thing")?;

    let path = &it.path;
    let content = fs::read(path)
        .with_context(|| format!("Failed to read instrs from {}", path.display()))?;

    Ok(content)
}
```

```text
Error: Failed to read instrs from ./path/to/instrs.json

Caused by:
    No such file or directory (os error 2)
```

--------------------------------

### Custom Error Rendering

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

This example shows how to manually render an error and its cause chain if the built-in representations are not sufficient. It iterates through the error chain using `err.chain()`.

```rust
use anyhow::{Context, Result};

fn main() {
    if let Err(err) = try_main() {
        eprintln!("ERROR: {}", err);
        err.chain().skip(1).for_each(|cause| eprintln!("because: {}", cause));
        std::process::exit(1);
    }
}

fn try_main() -> Result<()> {
    ...
}
```

--------------------------------

### Constructing an Error from a Boxed Error

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

This function constructs an `anyhow::Error` from a boxed standard library error that is `Send + Sync`. It handles the necessary vtable setup for the boxed error.

```APIDOC
## `construct_from_boxed`

### Description
Constructs an `anyhow::Error` from a `Box<dyn StdError + Send + Sync>`.

### Method
`pub(crate) fn construct_from_boxed(error: Box<dyn StdError + Send + Sync>, backtrace: Option<Backtrace>) -> Self`

### Parameters
- `error` (Box<dyn StdError + Send + Sync>): The boxed error to wrap.
- `backtrace` (Option<Backtrace>): An optional backtrace to associate with the error.

### Safety
This function is unsafe because the provided vtable must operate correctly on the boxed error type.
```

--------------------------------

### Parse Type Path with Identifier

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of type paths that start with an identifier. This is a common case for simple type names.

```rust
(type $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($ident:tt $($dup:tt)*) $i:ident $($rest:tt)*) => {
        $crate::__parse_ensure!(tpath $stack $bail ($($fuel)*) {($($buf)* $ident) $($parse)*} ($($rest)*) $($rest)*)
    }
```

--------------------------------

### Error Handling in Stream Processing

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

This example demonstrates using `Error::msg` to convert errors from a stream's item processing into `anyhow::Error`. It's suitable for iterator or stream combinators.

```rust
use anyhow::{Error, Result};
use futures::stream::{Stream, StreamExt, TryStreamExt};

async fn demo<S>(stream: S) -> Result<Vec<Output>>
where
    S: Stream<Item = Input>,
{
    stream
        .then(ffi::do_some_work) // returns Result<Output, &str>
        .map_err(Error::msg)
        .try_collect()
        .await
}
```

--------------------------------

### Getting Backtrace Reference

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Unsafely retrieves a reference to the `Backtrace` from an `ErrorImpl`. This function is compiled only when the `std` feature is enabled and attempts to get the backtrace, falling back to `None` if not available.

```rust
#[cfg(feature = "std")]
    pub(crate) unsafe fn backtrace(this: Ref<Self>) -> &Backtrace {
        // This unwrap can only panic if the underlying error's backtrace method
        // is nondeterministic, which would only happen in maliciously
        // constructed code.
        unsafe { this.deref() }
            .backtrace
            .as_ref()
            .or_else(|| {

```

--------------------------------

### Using Context on Option

Source: https://docs.rs/anyhow/latest/anyhow/trait.Context.html

Demonstrates how to use the `context` method on an `Option` to convert `None` into an `anyhow::Result` with a specific error message.

```rust
use anyhow::{Context, Result};

fn maybe_get() -> Option<T> {
    ...
}

fn demo() -> Result<()> {
    let t = maybe_get().context("there is no T")?;
    ...
}
```

--------------------------------

### Basic anyhow Usage

Source: https://docs.rs/anyhow/latest/src/anyhow/fmt.rs.html

Demonstrates the basic usage of the anyhow crate for error handling. This snippet shows how to create and return an anyhow::Error.

```rust
use anyhow::{Context, Result};

fn might_fail() -> Result<i32> {
    Ok(5)
}

fn main() {
    match might_fail() {
        Ok(value) => println!("Success: {}", value),
        Err(e) => println!("Error: {:?}", e),
    }
}
```

--------------------------------

### into_ok

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Returns the contained Ok value, but never panics. This is a nightly-only experimental API.

```APIDOC
## into_ok

### Description
Returns the contained `Ok` value, but never panics. This method is known to never panic on the result types it is implemented for.

### Method
`pub const fn into_ok(self) -> T`

### Constraints
`where E: Into<!>`

### Notes
This is a nightly-only experimental API.

### Examples
```
fn only_good_news() -> Result<String, !> {
    Ok("this is fine".into())
}

let s: String = only_good_news().into_ok();
println!("{s}");
```
```

--------------------------------

### AsRef<dyn StdError> for Error

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Implements AsRef to get a reference to a dynamic standard error.

```rust
impl AsRef<dyn StdError> for Error {
    fn as_ref(&self) -> &(dyn StdError + 'static) {
        &**self
    }
}
```

--------------------------------

### AsRef Implementations for StdError

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Provides `AsRef` implementations to get references to dynamic `StdError` types from `Error`.

```APIDOC
## `AsRef<dyn StdError + Send + Sync>` for `Error`

### Description
Allows getting a reference to `dyn StdError + Send + Sync` from an `Error`.

### Implementation
`impl AsRef<dyn StdError + Send + Sync> for Error`
```

```APIDOC
## `AsRef<dyn StdError>` for `Error`

### Description
Allows getting a reference to `dyn StdError` from an `Error`.

### Implementation
`impl AsRef<dyn StdError> for Error`
```

--------------------------------

### Formatting Errors with `Debug` and `Display`

Source: https://docs.rs/anyhow/latest/src/anyhow/fmt.rs.html

Explains how anyhow uses the `Debug` and `Display` traits for error formatting. The `{:?}` format specifier typically shows the full error chain with context, while `{}` shows the primary error message.

```rust
use anyhow::{Context, Result};

fn inner_function() -> Result<()>
{
    Err(anyhow::anyhow!("Inner error details")).context("Error in inner function")
}

fn outer_function() -> Result<()>
{
    inner_function().context("Error in outer function")
}

fn main() {
    match outer_function() {
        Ok(_) => println!("Operation successful."),
        Err(e) => {
            println!("Display format: {}", e); // Uses Display trait
            println!("Debug format: {:?}", e); // Uses Debug trait, shows chain
        }
    }
}
```

--------------------------------

### No-std Support Configuration

Source: https://docs.rs/anyhow/latest/anyhow/index.html

To use `anyhow` in a no-std environment, disable the default 'std' feature in your `Cargo.toml` and ensure a global allocator is available. This configuration is necessary for embedded or minimal environments.

```toml
[dependencies]
anyhow = { version = "1.0", default-features = false }
```

--------------------------------

### chain

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

Provides an iterator over the chain of source errors contained within this Error object, starting from the immediate source.

```APIDOC
## chain(&self) -> Chain<'_>

### Description
An iterator of the chain of source errors contained by this Error. This iterator will visit every error in the cause chain of this error object, beginning with the error that this error object was created from.
```

--------------------------------

### Error Reporting with `anyhow::Error`

Source: https://docs.rs/anyhow/latest/src/anyhow/fmt.rs.html

Illustrates how `anyhow::Error` provides a rich debugging output when formatted with `{:?}`, including the error chain and context added via `.context()`.

```rust
use anyhow::{Context, Result};

fn step_three() -> Result<()>
{
    Err(anyhow::anyhow!("Failed at the final step")).context("Step 3")
}

fn step_two() -> Result<()>
{
    step_three().context("Step 2")
}

fn step_one() -> Result<()>
{
    step_two().context("Step 1")
}

fn main() {
    match step_one() {
        Ok(_) => println!("Success!"),
        Err(e) => println!("Full error report:\n{:?}", e),
    }
}
```

--------------------------------

### Get Backtrace

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Retrieves the backtrace for the current error. Requires specific environment variables to be set for backtraces to be captured and meaningful.

```APIDOC
## backtrace

### Description
Get the backtrace for this Error.

In order for the backtrace to be meaningful, one of the two environment
variables `RUST_LIB_BACKTRACE=1` or `RUST_BACKTRACE=1` must be defined
and `RUST_LIB_BACKTRACE` must not be `0`. Backtraces are somewhat
expensive to capture in Rust, so we don't necessarily want to be
capturing them all over the place all the time.

- If you want panics and errors to both have backtraces, set
  `RUST_BACKTRACE=1`;
- If you want only errors to have backtraces, set
  `RUST_LIB_BACKTRACE=1`;
- If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
  `RUST_LIB_BACKTRACE=0`.

### Stability

Standard library backtraces are only available when using Rust &ge;
1.65. On older compilers, this function is only available if the crate's
"backtrace" feature is enabled, and will use the `backtrace` crate as
the underlying backtrace implementation. The return type of this
function on old compilers is `&(impl Debug + Display)`.

```toml
[dependencies]
anyhow = { version = "1.0", features = ["backtrace"] }
```

### Method
`pub fn backtrace(&self) -> &Backtrace`
```

--------------------------------

### Parse Ensure Macro: Epath with Identifier

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of path expressions starting with an identifier within the `__parse_ensure!` macro.

```rust
$crate::__parse_ensure!(epath (atom $stack) $bail ($($fuel)*) {($($buf)* $ident) $($parse)*} ($($rest)*) $($rest)*);
```

--------------------------------

### anyhow::Result Usage

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Demonstrates how to use anyhow::Result as a return type for functions, simplifying error propagation.

```APIDOC
## anyhow::Result

### Description
`anyhow::Result<T, E>` is a convenient return type for applications. When used as the return type for `fn main`, failures are printed along with context and a backtrace if captured.

`anyhow::Result` can be used with one or two type parameters:

### Method
Type Alias

### Usage Examples
```rust
use anyhow::Result;

// Equivalent to std::result::Result<T, anyhow::Error>
fn demo1() -> Result<T> { ... }

// Equivalent to std::result::Result<T, OtherError>
fn demo2() -> Result<T, OtherError> { ... }
```

### Example
```rust
use anyhow::Result;

fn main() -> Result<()> {
    let config = std::fs::read_to_string("cluster.json")?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    println!("cluster info: {:#?}", map);
    Ok(())
}
```
```

--------------------------------

### AsRef<dyn StdError + Send + Sync> for Error

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Implements AsRef to get a reference to a dynamic standard error that is Send and Sync.

```rust
impl AsRef<dyn StdError + Send + Sync> for Error {
    fn as_ref(&self) -> &(dyn StdError + Send + Sync + 'static) {
        &**self
    }
}
```

--------------------------------

### take

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Creates an iterator that yields the first `n` elements, or fewer if the underlying iterator ends sooner.

```APIDOC
## fn take(self, n: usize) -> Take<Self>

### Description
Creates an iterator that yields the first `n` elements, or fewer if the underlying iterator ends sooner.

### Parameters
- **n**: The number of elements to take.

### Type Constraints
- `Self`: Must implement `Sized`.
```

--------------------------------

### Enabling Backtraces with `anyhow` Crate Feature

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

Illustrates how to enable backtraces for `anyhow::Error` by adding the `"backtrace"` feature to the `anyhow` dependency in `Cargo.toml`. Backtraces are useful for debugging but can incur performance costs.

```toml
[dependencies]
anyhow = { version = "1.0", features = ["backtrace"] }
```

--------------------------------

### Error Chain Iterator

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Provides an iterator over the chain of source errors contained within this Error object, starting from the immediate cause.

```APIDOC
## chain

### Description
An iterator of the chain of source errors contained by this Error.

This iterator will visit every error in the cause chain of this error
object, beginning with the error that this error object was created
from.

### Example

```
use anyhow::Error;
use std::io;

pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
    for cause in error.chain() {
        if let Some(io_error) = cause.downcast_ref::<io::Error>() {
            return Some(io_error.kind());
        }
    }
    None
}
```

### Method
`pub fn chain(&self) -> Chain`
```

--------------------------------

### Adding Context to File Operations

Source: https://docs.rs/anyhow/latest/src/anyhow/lib.rs.html

Demonstrates adding context to errors during file operations using `context` and `with_context`. Imports `anyhow::Context` and `std::fs`.

```rust
use anyhow::{Context, Result};
use std::fs;
use std::path::PathBuf;

pub struct ImportantThing {
    path: PathBuf,
}

impl ImportantThing {
    # const IGNORE: &'static str = stringify! {
    pub fn detach(&mut self) -> Result<()> {...}
    # };
    # fn detach(&mut self) -> Result<()> {
    #     unimplemented!()
    # }
}

pub fn do_it(mut it: ImportantThing) -> Result<Vec<u8>> {
    it.detach().context("Failed to detach the important thing")?;

    let path = &it.path;
    let content = fs::read(path)
        .with_context(|| format!("Failed to read instrs from {}", path.display()))?;

    Ok(content)
}

```

--------------------------------

### unwrap_err() on Err Result

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `unwrap_err()` to get the contained error value when you are certain the Result is Err. This method panics if the Result is Ok.

```rust
let x: Result<u32, &str> = Err("emergency failure");
assert_eq!(x.unwrap_err(), "emergency failure");
```

--------------------------------

### Alternate Display Representation

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

Using the alternate selector `{:#}` prints causes as well, showing the error chain with anyhow's default formatting.

```text
Failed to read instrs from ./path/to/instrs.json: No such file or directory (os error 2)
```

--------------------------------

### Basic unwrap on Ok Result

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `unwrap()` to get the contained value when you are certain the Result is Ok. This method panics if the Result is Err.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.unwrap(), 2);
```

--------------------------------

### Get reference to Result contents

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `as_ref()` to obtain references to the contained values of a Result without consuming it. This is useful for inspecting values.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.as_ref(), Ok(&2));

let x: Result<u32, &str> = Err("Error");
assert_eq!(x.as_ref(), Err(&"Error"));
```

--------------------------------

### Iterating and Calculating Product with Result

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Demonstrates how to use the `product` method on an iterator of Results. If any element fails to parse, the entire operation returns an Err. Otherwise, it returns the Ok value of the product.

```rust
let nums = vec!["5", "10", "1", "2"];
let total: Result<usize, _> = nums.iter().map(|w| w.parse::<usize>()).product();
assert_eq!(total, Ok(100));
```

```rust
let nums = vec!["5", "10", "one", "2"];
let total: Result<usize, _> = nums.iter().map(|w| w.parse::<usize>()).product();
assert!(total.is_err());
```

--------------------------------

### Parse Ensure Macro: Epath with Colons and Identifier

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of path expressions starting with colons and an identifier within the `__parse_ensure!` macro.

```rust
$crate::__parse_ensure!(epath (atom $stack) $bail ($($fuel)*) {($($buf)* $colons $ident) $($parse)*} ($($rest)*) $($rest)*);
```

--------------------------------

### Adhoc::new Method

Source: https://docs.rs/anyhow/latest/src/anyhow/kind.rs.html

Constructs an anyhow::Error from a message that only requires Display and Debug. It captures a backtrace.

```rust
impl Adhoc {
    #[cold]
    pub fn new<M>(self, message: M) -> Error
    where
        M: Display + Debug + Send + Sync + 'static,
    {
        Error::construct_from_adhoc(message, Some(std::backtrace::Backtrace::capture())backtrace!()) 
    }
}
```

--------------------------------

### Getting Mutable StdError Reference

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Unsafely retrieves a mutable reference to the underlying `StdError` from an `ErrorImpl`. This is conditionally compiled based on the `std` or `core_error` features.

```rust
#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
    pub(crate) unsafe fn error_mut(this: Mut<Self>) -> &mut (dyn StdError + Send + Sync + 'static) {
        // Use vtable to attach E's native StdError vtable for the right
        // original type E.
        unsafe {
            (vtable(this.ptr).object_ref)(this.by_ref())
                .by_mut()
                .deref_mut()
        }
    }
```

--------------------------------

### Function Signature for Ok

Source: https://docs.rs/anyhow/latest/anyhow/fn.Ok.html

This is the function signature for `anyhow::fn::Ok`. It takes a value of any type `T` and returns a `Result<T>`.

```rust
pub fn Ok<T>(value: T) -> Result<T>
```

--------------------------------

### Parse Type Path with Angle Bracket

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of type paths that are followed by an opening angle bracket '<', indicating the start of generic parameters.

```rust
(type $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($langle:tt $($dup:tt)*) < $($rest:tt)*) => {
        $crate::__parse_ensure!(type (qpath (tpath $stack)) $bail ($($fuel)*) {($($buf)* $langle) $($parse)*} ($($rest)*) $($rest)*)
    }
```

--------------------------------

### Boxed::new Method

Source: https://docs.rs/anyhow/latest/src/anyhow/kind.rs.html

Constructs an anyhow::Error from a boxed dynamic error. It attempts to capture a backtrace if possible, otherwise uses a captured backtrace.

```rust
#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
impl Boxed {
    #[cold]
    pub fn new(self, error: Box<dyn StdError + Send + Sync>) -> Error {
        let backtrace = match crate::nightly::request_ref_backtrace(&*error as
            &dyn core::error::Error) {
    Some(_) => None,
    None => Some(std::backtrace::Backtrace::capture()),
}backtrace_if_absent!(&*error);
        Error::construct_from_boxed(error, backtrace)
    }
}
```

--------------------------------

### Getting StdError Reference

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Unsafely retrieves a reference to the underlying `StdError` from an `ErrorImpl` using its vtable. This allows interacting with the error as a standard Rust error type.

```rust
impl ErrorImpl {
    pub(crate) unsafe fn error(this: Ref<Self>) -> &(dyn StdError + Send + Sync + 'static) {
        // Use vtable to attach E's native StdError vtable for the right
        // original type E.
        unsafe { (vtable(this.ptr).object_ref)(this).deref() }
    }
}
```

--------------------------------

### partition

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Consumes an iterator and creates two collections based on a predicate.

```APIDOC
## fn partition<B, F>(self, f: F) -> (B, B)

### Description
Consumes an iterator, creating two collections from it based on a predicate.

### Method
`partition`

### Parameters
- `f` (F): A closure that takes an item and returns a boolean.

### Type Parameters
- `B`: The type of the collections, which must implement `Default` and `Extend<Self::Item>`.

### Returns
- `(B, B)`: A tuple containing two collections: one for elements where the predicate returned `true`, and one for elements where it returned `false`.
```

--------------------------------

### Parse Type Path with Colons and Angle Bracket

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of type paths starting with '::<' which is used for associated types or specific generic path syntaxes.

```rust
(tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $langle:tt $($dup:tt)*) :: < $($rest:tt)*) => {
        $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* $colons $langle) $($parse)*} ($($rest)*) $($rest)*)
    }
```

--------------------------------

### partition_in_place

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Reorders elements in-place based on a predicate. This is a nightly-only experimental API.

```APIDOC
## fn partition_in_place<'a, T, P>(self, predicate: P) -> usize

### Description
Reorders the elements of this iterator _in-place_ according to the given predicate, such that all those that return `true` precede all those that return `false`. Returns the number of `true` elements found.

### Method
`partition_in_place`

### Parameters
- `predicate` (P): A closure that takes a reference to an element and returns a boolean.

### Type Parameters
- `'a`: Lifetime parameter.
- `T`: The type of the elements in the iterator.
- `P`: The type of the predicate closure.

### Returns
- `usize`: The number of elements for which the predicate returned `true`.

### Notes
This is a nightly-only experimental API.
```

--------------------------------

### Get Root Cause of an Error

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Retrieves the lowest-level cause of an Anyhow error, which is the last error in the chain produced by `chain()`. This requires the `std` feature or `anyhow_no_core_error` to be disabled.

```rust
#[cfg(any(feature = "std", not(anyhow_no_core_error)))]
#[allow(clippy::double_ended_iterator_last)]
pub fn root_cause(&self) -> &(dyn StdError + 'static) {
    self.chain().last().unwrap()
}
```

--------------------------------

### Convert Result to Option (Ok value)

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `ok()` to convert a Result into an Option, retaining the Ok value if present. Errors are converted to None.

```rust
let x: Result<u32, &str> = Ok(2);
assert_eq!(x.ok(), Some(2));

let x: Result<u32, &str> = Err("Nothing here");
assert_eq!(x.ok(), None);
```

--------------------------------

### Default for Chain

Source: https://docs.rs/anyhow/latest/src/anyhow/chain.rs.html

Provides a default empty `Chain`.

```APIDOC
## Default for Chain

### Description
Creates an empty `Chain` with no errors. This is useful for initializing a `Chain` when no error is present initially.

### Method
`default`

### Return Value
- `Chain<'a>` - An empty `Chain` instance.
```

--------------------------------

### unwrap_or_default() for default values

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `unwrap_or_default()` to get the contained Ok value or the type's default value if the Result is Err. This is useful for fallbacks when a default is acceptable.

```rust
let good_year_from_input = "1909";
let bad_year_from_input = "190blarg";
let good_year = good_year_from_input.parse().unwrap_or_default();
let bad_year = bad_year_from_input.parse().unwrap_or_default();

assert_eq!(1909, good_year);
assert_eq!(0, bad_year);
```

--------------------------------

### Get mutable reference to Result contents

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Use `as_mut()` to obtain mutable references to the contained values of a Result. This allows in-place modification of Ok or Err values.

```rust
fn mutate(r: &mut Result<i32, i32>) {
    match r.as_mut() {
        Ok(v) => *v = 42,
        Err(e) => *e = 0,
    }
}

let mut x: Result<i32, i32> = Ok(2);
mutate(&mut x);
assert_eq!(x.unwrap(), 42);

let mut x: Result<i32, i32> = Err(13);
mutate(&mut x);
assert_eq!(x.unwrap_err(), 0);
```

--------------------------------

### by_ref

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Creates a “by reference” adapter for this instance of `Iterator`.

```APIDOC
## fn by_ref(&mut self) -> &mut Self

### Description
Creates a “by reference” adapter for this instance of `Iterator`.

### Type Constraints
- `Self`: Must implement `Sized`.
```

--------------------------------

### Parse Type Path with Colons and Double Angle Brackets

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of type paths starting with '::<<', used for complex associated types or nested generic structures.

```rust
(tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $langle:tt $($dup:tt)*) :: << $($rest:tt)*) => {
        $crate::__parse_ensure!(type (qpath (tpath (arglist (tpath $stack)))) $bail ($($fuel)*) {($($buf)* $colons $langle) $($parse)*} ($($rest)*) $($rest)*)
    }
```

--------------------------------

### map_windows

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Calls the given function `f` for each contiguous window of size `N` over `self` and returns an iterator over the outputs of `f`. This is a nightly-only experimental API.

```APIDOC
## fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N>

### Description
Calls the given function `f` for each contiguous window of size `N` over `self` and returns an iterator over the outputs of `f`.

### Parameters
- **f**: The function to apply to each window.

### Type Constraints
- `Self`: Must implement `Sized`.
- `F`: Must implement `FnMut(&[Self::Item; N]) -> R`.
- `N`: The size of the window.
```

--------------------------------

### Parse Ensure Macro: Epath with Colons and Angle Brackets

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of path expressions starting with colons and followed by angle brackets within the `__parse_ensure!` macro.

```rust
$crate::__parse_ensure!(generic (epath $stack) $bail ($($fuel)*) {($($buf)* $colons $langle) $($parse)*} ($($rest)*) $($rest)*);
```

--------------------------------

### product

Source: https://docs.rs/anyhow/latest/anyhow/struct.Chain.html

Iterates over the entire iterator, multiplying all the elements.

```APIDOC
## product<P>(self) -> P

### Description
Iterates over the entire iterator, multiplying all the elements. The product type `P` must implement `Product`.
```

--------------------------------

### anyhow Macro Definition

Source: https://docs.rs/anyhow/latest/anyhow/macro.anyhow.html

Defines the different forms the anyhow macro can take, including literal strings, expressions, and formatted strings with arguments.

```rust
macro_rules! anyhow {
    ($msg:literal $(,)?) => { ... };
    ($err:expr $(,)?) => { ... };
    ($fmt:expr, $($arg:tt)*) => { ... };
}
```

--------------------------------

### Parse Type Path with Colons and Identifier

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of qualified type paths that start with '::' followed by an identifier, used for accessing items within modules or associated items.

```rust
(tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $ident:tt $($dup:tt)*) :: $i:ident $($rest:tt)*) => {
        $crate::__parse_ensure!(tpath $stack $bail ($($fuel)*) {($($buf)* $colons $ident) $($parse)*} ($($rest)*) $($rest)*)
    }
```

--------------------------------

### Adding Context to Errors

Source: https://docs.rs/anyhow/latest/src/anyhow/fmt.rs.html

Illustrates how to add context to errors using the `context` method provided by anyhow. This is useful for providing more information about where an error occurred.

```rust
use anyhow::{Context, Result};

fn read_config() -> Result<String> {
    // Simulate reading a config file that might not exist
    Err(anyhow::anyhow!("Config file not found")).context("Failed to read configuration")
}

fn main() {
    match read_config() {
        Ok(config) => println!("Config: {}", config),
        Err(e) => println!("Error: {:?}", e),
    }
}
```

--------------------------------

### Context and Downcasting

Source: https://docs.rs/anyhow/latest/anyhow/trait.Context.html

Explains how adding context with `anyhow::Context` affects downcasting. It ensures that existing downcasts will continue to work, supporting both cases where the context type is significant for downcasting or insignificant.

```APIDOC
## §Effect on downcasting
After attaching context of type `C` onto an error of type `E`, the resulting `anyhow::Error` may be downcast to `C` **or** to `E`.

### Attaching context whose type is insignificant onto errors whose type is used in downcasts.
```rust
use anyhow::{Context, Result};

fn do_it() -> Result<()> {
    helper().context("Failed to complete the work")?;
    ...
}

fn main() {
    let err = do_it().unwrap_err();
    if let Some(e) = err.downcast_ref::<SuspiciousError>() {
        // If helper() returned SuspiciousError, this downcast will
        // correctly succeed even with the context in between.
    }
}
```

### Attaching context whose type is used in downcasts onto errors whose type is insignificant.
```rust
use anyhow::{Context, Result};

fn do_it() -> Result<()> {
    helper().context(HelperFailed)?;
    ...
}

fn main() {
    let err = do_it().unwrap_err();
    if let Some(e) = err.downcast_ref::<HelperFailed>() {
        // If helper failed, this downcast will succeed because
        // HelperFailed is the context that has been attached to
        // that error.
    }
}
```
```

--------------------------------

### Parse Ensure Macro: Epath with Colons and Identifier (revisited)

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of path expressions starting with colons and an identifier, revisiting a previous pattern within the `__parse_ensure!` macro.

```rust
$crate::__parse_ensure!(epath $stack $bail ($($fuel)*) {($($buf)* $colons $ident) $($parse)*} ($($rest)*) $($rest)*);
```

--------------------------------

### Parse Ensure Macro: Epath with Colons and Left Arrow

Source: https://docs.rs/anyhow/latest/src/anyhow/ensure.rs.html

Handles parsing of path expressions starting with colons and a left arrow, followed by a literal, within the `__parse_ensure!` macro.

```rust
$crate::__parse_ensure!(generic (epath $stack) $bail ($($fuel)*) {($($buf)* $colons $larrow) $($parse)*} ($($dup)*) $($dup)*);
```

--------------------------------

### Result Implementations

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Common implementations for the Result type, including methods for copying, cloning, transposing, and flattening.

```APIDOC
## Implementations

### `impl<T, E> Result<&T, E>`

#### `copied(self) -> Result<T, E>`

*   **Description**: Maps a `Result<&T, E>` to a `Result<T, E>` by copying the contents of the `Ok` part. Requires `T: Copy`.
*   **Example**:
    ```rust
    let val = 12;
    let x: Result<&i32, i32> = Ok(&val);
    let copied = x.copied();
    assert_eq!(copied, Ok(12));
    ```

#### `cloned(self) -> Result<T, E>`

*   **Description**: Maps a `Result<&T, E>` to a `Result<T, E>` by cloning the contents of the `Ok` part. Requires `T: Clone`.
*   **Example**:
    ```rust
    let val = 12;
    let x: Result<&i32, i32> = Ok(&val);
    let cloned = x.cloned();
    assert_eq!(cloned, Ok(12));
    ```

### `impl<T, E> Result<&mut T, E>`

#### `copied(self) -> Result<T, E>`

*   **Description**: Maps a `Result<&mut T, E>` to a `Result<T, E>` by copying the contents of the `Ok` part. Requires `T: Copy`.
*   **Example**:
    ```rust
    let mut val = 12;
    let x: Result<&mut i32, i32> = Ok(&mut val);
    let copied = x.copied();
    assert_eq!(copied, Ok(12));
    ```

#### `cloned(self) -> Result<T, E>`

*   **Description**: Maps a `Result<&mut T, E>` to a `Result<T, E>` by cloning the contents of the `Ok` part. Requires `T: Clone`.
*   **Example**:
    ```rust
    let mut val = 12;
    let x: Result<&mut i32, i32> = Ok(&mut val);
    let cloned = x.cloned();
    assert_eq!(cloned, Ok(12));
    ```

### `impl<T, E> Result<Option<T>, E>`

#### `transpose(self) -> Option<Result<T, E>>`

*   **Description**: Transposes a `Result` of an `Option` into an `Option` of a `Result`. `Ok(None)` maps to `None`. `Ok(Some(_))` and `Err(_)` map to `Some(Ok(_))` and `Some(Err(_))` respectively.
*   **Example**:
    ```rust
    #[derive(Debug, Eq, PartialEq)]
    struct SomeErr;
    let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
    let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
    assert_eq!(x.transpose(), y);
    ```

### `impl<T, E> Result<Result<T, E>, E>`

#### `flatten(self) -> Result<T, E>`

*   **Description**: Converts from `Result<Result<T, E>, E>` to `Result<T, E>`, removing one level of nesting.
*   **Example**:
    ```rust
    let x: Result<Result<&'static str, u32>, u32> = Ok(Ok("hello"));
    assert_eq!(Ok("hello"), x.flatten());

    let x: Result<Result<&'static str, u32>, u32> = Ok(Err(6));
    assert_eq!(Err(6), x.flatten());

    let x: Result<Result<&'static str, u32>, u32> = Err(6);
    assert_eq!(Err(6), x.flatten());
    ```

### `impl<T, E> Result<T, E>`

#### `is_ok(&self) -> bool`

*   **Description**: Returns `true` if the result is `Ok`.
*   **Example**:
    ```rust
    let x: Result<i32, &str> = Ok(-3);
    assert_eq!(x.is_ok(), true);

    let x: Result<i32, &str> = Err("Some error message");
    assert_eq!(x.is_ok(), false);
    ```

#### `is_ok_and<F>(self, f: F) -> bool` where `F: FnOnce(T) -> bool`

*   **Description**: Returns `true` if the result is `Ok` and the value inside it matches a predicate.
*   **Example**:
    ```rust
    let x: Result<u32, &str> = Ok(2);
    assert_eq!(x.is_ok_and(|x| x > 1), true);

    let x: Result<u32, &str> = Ok(0);
    assert_eq!(x.is_ok_and(|x| x > 1), false);

    let x: Result<u32, &str> = Err("hey");
    assert_eq!(x.is_ok_and(|x| x > 1), false);
    ```

#### `is_err(&self) -> bool`

*   **Description**: Returns `true` if the result is `Err`.
```

--------------------------------

### Iterating Through Error Causes with `chain()`

Source: https://docs.rs/anyhow/latest/anyhow/struct.Error.html

Demonstrates how to use the `chain()` method to iterate over all source errors in an `anyhow::Error`'s cause chain. This is useful for inspecting or handling specific error types within the chain.

```rust
use anyhow::Error;
use std::io;

pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
    for cause in error.chain() {
        if let Some(io_error) = cause.downcast_ref::<io::Error>() {
            return Some(io_error.kind());
        }
    }
    None
}
```

--------------------------------

### Construct Error from Boxed StdError

Source: https://docs.rs/anyhow/latest/src/anyhow/error.rs.html

Used internally to construct an anyhow::Error from a boxed standard library error. Requires specific vtable setup for the boxed error type.

```rust
unsafe { Error::construct(error, vtable, backtrace) }
```

--------------------------------

### Using anyhow::Result in Functions

Source: https://docs.rs/anyhow/latest/anyhow/type.Result.html

Demonstrates how to use anyhow::Result as a return type in functions. It's equivalent to std::result::Result<T, anyhow::Error> or std::result::Result<T, OtherError>.

```rust
use anyhow::Result;

fn demo1() -> Result<T> {...}
           // ^ equivalent to std::result::Result<T, anyhow::Error>

fn demo2() -> Result<T, OtherError> {...}
           // ^ equivalent to std::result::Result<T, OtherError>
```