### Complete Example: Index-Based Data Access

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Demonstrates combining `AsRefWithContext` and `DisplayWithContext` traits for flexible index-based data access. This example shows how an `Index` struct can be used with different contexts like string slices and `Vec<String>`.

```rust
use contextual::{WithContext, AsRefWithContext, DisplayWithContext};
use std::fmt;

/// Represents an index into a collection stored in context
#[derive(Clone, Copy, Debug)]
pub struct Index(pub usize);

// Implement AsRefWithContext for generic slice access
impl<T, C: AsRef<[T]>> AsRefWithContext<T, C> for Index {
    fn as_ref_with<'a>(&'a self, context: &'a C) -> &'a T {
        &context.as_ref()[self.0]
    }
}

// Implement DisplayWithContext for string slice contexts
impl<'a, C: AsRef<[&'a str]>> DisplayWithContext<C> for Index {
    fn fmt_with(&self, context: &C, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", context.as_ref()[self.0])
    }
}

fn main() {
    let i = Index(1);
    let context = ["a", "b", "c"];

    // Display via format macro
    let output = format!("index: {}", i.with(&context));
    assert_eq!(output, "index: b");

    // AsRef access
    let value: &str = *i.with(&context).as_ref();
    assert_eq!(value, "b");

    // Works with Vec too
    let vec_context = vec!["x", "y", "z"];
    println!("From vec: {}", i.with(&vec_context));
}
```

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

### Implement TryFromWithContext for ValidatedSymbol

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Implement `TryFromWithContext` for fallible conversions, returning a `Result`. This example shows converting a string slice to a `ValidatedSymbol` using a `SymbolRegistry` context, with `SymbolNotFound` as the error type.

```rust
use contextual::{TryFromWithContext, TryIntoWithContext};
use std::collections::HashMap;

#[derive(Debug, PartialEq)]
struct ValidatedSymbol(u32);

#[derive(Debug, PartialEq)]
struct SymbolNotFound(String);

struct SymbolRegistry(HashMap<String, u32>);

impl TryFromWithContext<&str, SymbolRegistry> for ValidatedSymbol {
    type Error = SymbolNotFound;

    fn try_from_with(value: &str, context: &SymbolRegistry) -> Result<Self, Self::Error> {
        context.0
            .get(value)
            .map(|&id| ValidatedSymbol(id))
            .ok_or_else(|| SymbolNotFound(value.to_string()))
    }
}

let mut registry = HashMap::new();
registry.insert("valid".to_string(), 42);
let context = SymbolRegistry(registry);

// Successful conversion
let result: Result<ValidatedSymbol, _> = "valid".try_into_with(&context);
assert_eq!(result, Ok(ValidatedSymbol(42)));

// Failed conversion
let result: Result<ValidatedSymbol, _> = "invalid".try_into_with(&context);
assert_eq!(result, Err(SymbolNotFound("invalid".to_string())));
```

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

### Implement IntoRefWithContext for StringId

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Implement `IntoRefWithContext` to consume a value and produce a reference with the context's lifetime. This example converts a `StringId` to a `&str` using a `Vec<String>` context.

```rust
use contextual::{WithContext, IntoRefWithContext};

/// A string ID that can be converted to a string slice from context
#[derive(Clone, Copy)]
struct StringId(usize);

impl<'a> IntoRefWithContext<'a, str, Vec<String>> for StringId {
    fn into_ref_with(self, context: &'a Vec<String>) -> &'a str {
        &context[self.0]
    }
}

let strings = vec![
    "hello".to_string(),
    "world".to_string(),
];

let id = StringId(0);

// The into_str() convenience method consumes the Contextual wrapper
let s: &str = id.with(&strings).into_str();
assert_eq!(s, "hello");

// The original id can be reused since StringId is Copy
let s2: &str = id.with(&strings).into_str();
assert_eq!(s2, "hello");
```

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

### Implement DisplayWithContext for Contextual Formatting

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Implement DisplayWithContext to enable context-aware formatting for types. The Contextual wrapper automatically implements std::fmt::Display.

```rust
use contextual::{WithContext, DisplayWithContext};
use std::fmt;

/// An index that displays the value from context when formatted
struct NameIndex(usize);

impl<C: AsRef<[&'static str]>> DisplayWithContext<C> for NameIndex {
    fn fmt_with(&self, context: &C, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", context.as_ref()[self.0])
    }
}

let names = ["Alice", "Bob", "Charlie"];
let idx = NameIndex(2);

// The Contextual wrapper implements Display
let message = format!("Hello, {}!", idx.with(&names));
assert_eq!(message, "Hello, Charlie!");

// Works with print macros
println!("Selected: {}", idx.with(&names));

// DisplayWithContext is also implemented for references and Cow types
let idx_ref = &idx;
println!("Via reference: {}", idx_ref.with(&names));
```

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

### Implement Contextual Traits in Rust

Source: https://github.com/timothee-haudebourg/contextual/blob/main/README.md

Demonstrates implementing AsRefWithContext and DisplayWithContext for an Index struct to access and display data from a slice context.

```rust
use contextual::{WithContext, AsRefWithContext, DisplayWithContext};
use std::fmt;

/// Index of an element in some array.
pub struct Index(usize);

impl<T, C: AsRef<[T]>> AsRefWithContext<T, C> for Index {
  fn as_ref_with<'a>(&'a self, context: &'a C) -> &'a T {
    &context.as_ref()[self.0]
  }
}

impl<'a, C: AsRef<[&'a str]>> DisplayWithContext<C> for Index {
  fn fmt_with(&self, context: &C, f: &mut fmt::Formatter) -> fmt::Result {
    use fmt::Display;
    context.as_ref()[self.0].fmt(f)
  }
}

let i = Index(1);
let context = ["a", "b", "c"];

print!("index: {}", i.with(&context));
assert_eq!(*i.with(&context).as_ref(), "b")
```

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

### Implement AsRefWithContext for Contextual References

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Implement AsRefWithContext to allow types to return references to data stored in a context. The Contextual wrapper automatically implements AsRef.

```rust
use contextual::{WithContext, AsRefWithContext};

/// A simple index type that references elements in a slice context
struct Index(usize);

impl<T, C: AsRef<[T]>> AsRefWithContext<T, C> for Index {
    fn as_ref_with<'a>(&'a self, context: &'a C) -> &'a T {
        &context.as_ref()[self.0]
    }
}

let items = ["first", "second", "third"];
let idx = Index(1);

// Use .with() to create a Contextual, then .as_ref() works automatically
let contextual = idx.with(&items);
let value: &str = *contextual.as_ref();
assert_eq!(value, "second");
```

```rust
/// For string contexts, the as_str() convenience method is available
struct StringIndex(usize);

impl<C: AsRef<[&'static str]>> AsRefWithContext<str, C> for StringIndex {
    fn as_ref_with<'a>(&'a self, context: &'a C) -> &'a str {
        context.as_ref()[self.0]
    }
}

let words = ["hello", "world"];
let idx = StringIndex(0);
assert_eq!(idx.with(&words).as_str(), "hello");
```

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

### Implement FromWithContext for Symbol

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Implement `FromWithContext` to create a `Symbol` from a string slice using a `SymbolTable` context. This automatically provides `IntoWithContext`.

```rust
use contextual::{FromWithContext, IntoWithContext};
use std::collections::HashMap;

/// A symbol that can be created from a string using a symbol table context
#[derive(Debug, PartialEq)]
struct Symbol(u32);

/// The context: a mapping from strings to symbol IDs
struct SymbolTable(HashMap<String, u32>);

impl FromWithContext<&str, SymbolTable> for Symbol {
    fn from_with(value: &str, context: &SymbolTable) -> Self {
        Symbol(*context.0.get(value).unwrap_or(&0))
    }
}

let mut table = HashMap::new();
table.insert("foo".to_string(), 1);
table.insert("bar".to_string(), 2);
let context = SymbolTable(table);

// Use FromWithContext directly
let sym1 = Symbol::from_with("foo", &context);
assert_eq!(sym1, Symbol(1));

// Use IntoWithContext (automatically available)
let sym2: Symbol = "bar".into_with(&context);
assert_eq!(sym2, Symbol(2));

// Unknown symbols get default value
let sym3: Symbol = "unknown".into_with(&context);
assert_eq!(sym3, Symbol(0));
```

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

### Create Contextual Wrappers with WithContext

Source: https://context7.com/timothee-haudebourg/contextual/llms.txt

Use the WithContext trait to create Contextual wrappers for references or owned values, enabling context-aware operations.

```rust
use contextual::WithContext;

// Any type can use the WithContext trait
let index: usize = 1;
let context = vec!["apple", "banana", "cherry"];

// Create a Contextual wrapper using .with() for references
let contextual_ref = index.with(&context);

// Create a Contextual wrapper using .into_with() for owned values
let contextual_owned = index.into_with(&context);

// The Contextual struct implements Deref, so you can access the inner value
assert_eq!(*contextual_ref, 1);
```

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