### Initialize DashMap with Custom Hasher (Rust)

Source: https://context7.com/xacrimon/dashmap/llms.txt

Shows how to create a DashMap using a custom hash builder, such as `RandomState`. This allows for specialized hashing strategies. The examples demonstrate initializing with just a hasher, or with hasher combined with capacity and shard count for performance tuning.

```rust
use dashmap::DashMap;
use std::collections::hash_map::RandomState;
use std::hash::BuildHasher;

// Use custom hasher
let hasher = RandomState::new();
let map = DashMap::with_hasher(hasher);
map.insert("key", "value");

// With capacity and hasher
let map = DashMap::with_capacity_and_hasher(1000, RandomState::new());

// With shard amount and hasher for fine control
let map = DashMap::with_hasher_and_shard_amount(RandomState::new(), 16);

// Full control over capacity, hasher, and shards
let map = DashMap::with_capacity_and_hasher_and_shard_amount(
    1000,
    RandomState::new(),
    32,
);
map.insert(42, "answer");
```

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

### Reading Values from DashMap (Rust)

Source: https://context7.com/xacrimon/dashmap/llms.txt

Explains how to read values from a DashMap. Includes methods for getting immutable references (`get`), mutable references (`get_mut`), non-blocking checks (`try_get`), and checking for key existence (`contains_key`).

```rust
use dashmap::DashMap;

let map = DashMap::new();
map.insert("rust", "fast");
map.insert("go", "simple");

// Get immutable reference
if let Some(value) = map.get("rust") {
    assert_eq!(*value, "fast");
    // value is a Ref guard, automatically releases lock when dropped
}

// Get mutable reference
if let Some(mut value) = map.get_mut("go") {
    *value = "concurrent";
}
assert_eq!(*map.get("go").unwrap(), "concurrent");

// Non-blocking try operations
match map.try_get("rust") {
    dashmap::try_result::TryResult::Present(val) => println!("{}", *val),
    dashmap::try_result::TryResult::Absent => println!("Not found"),
    dashmap::try_result::TryResult::Locked => println!("Shard locked, try later"),
}

// Check existence without locking value
assert!(map.contains_key("rust"));
```

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

### DashMap Advanced Entry API: Manipulate, Insert, and Compute Entries

Source: https://context7.com/xacrimon/dashmap/llms.txt

Demonstrates advanced entry manipulation in DashMap, including modifying existing entries, inserting default values if absent, and computing values with error handling. It shows how to get a mutable reference to an entry or insert a new one.

```rust
use dashmap::DashMap;

let map = DashMap::new();

// Complex entry manipulation
let entry = map.entry("user_id");
entry
    .and_modify(|id| *id += 1)
    .or_insert(1000);

// Pattern: increment counter or initialize
let mut counter_ref = map
    .entry("page_views")
    .or_insert(0);
*counter_ref += 1;

// Pattern: try to compute value, handle errors
let result = map.entry("config").or_try_insert_with(|| {
    load_config().map_err(|e| format!("Config error: {}", e))
});

match result {
    Ok(config_ref) => println!("Config loaded"),
    Err(e) => println!("Failed: {}", e),
}

// Insert and get entry
let occupied = map.entry("status").insert_entry("active".to_string());
assert_eq!(occupied.key(), &"status");

fn load_config() -> Result<String, std::io::Error> {
    Ok("loaded".to_string())
}
```

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

### Iterating Over DashMap Entries (Rust)

Source: https://context7.com/xacrimon/dashmap/llms.txt

Provides examples of iterating over the entries in a DashMap. It includes immutable iteration using `&map` and `iter()`, mutable iteration with `iter_mut()`, and consuming iteration by taking ownership of the map.

```rust
use dashmap::DashMap;

let map = DashMap::new();
map.insert("x", 10);
map.insert("y", 20);
map.insert("z", 30);

// Immutable iteration
for entry in &map {
    println!("{}: {}", entry.key(), entry.value());
}

// Explicit immutable iterator
for entry in map.iter() {
    let (key, value) = entry.pair();
    println!("{}: {}", key, value);
}

// Mutable iteration
map.iter_mut().for_each(|mut entry| {
    *entry.value_mut() *= 2;
});
assert_eq!(*map.get("x").unwrap(), 20);

// Consuming iteration
let owned_map = DashMap::new();
owned_map.insert(1, "one");
owned_map.insert(2, "two");

for (key, value) in owned_map {
    println!("{}: {}", key, value);
}
```

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

### Creating and Sharing DashMaps in Rust

Source: https://context7.com/xacrimon/dashmap/llms.txt

Demonstrates various ways to initialize a DashMap, including with default settings, a specific capacity, or a custom shard amount. It also shows how to share a DashMap across threads using Arc for safe concurrent access.

```rust
use dashmap::DashMap;
use std::sync::Arc;
use std::thread;

// Create a new empty DashMap
let map = DashMap::new();

// Create with specific capacity
let map = DashMap::with_capacity(100);

// Create with custom shard amount for fine-tuned concurrency
let map = DashMap::with_shard_amount(32);

// Share across threads using Arc
let map = Arc::new(DashMap::new());
let map_clone = Arc::clone(&map);

thread::spawn(move || {
    map_clone.insert("key", "value");
});

map.insert("another", "entry");
```

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

### DashMap Capacity Management: Reserve and Shrink

Source: https://context7.com/xacrimon/dashmap/llms.txt

Details capacity management in DashMap, showing how to reserve memory for future insertions and shrink the map's capacity to fit its current size. It also demonstrates checking the map's capacity and size.

```rust
use dashmap::DashMap;

let mut map = DashMap::new();
assert_eq!(map.capacity(), 0);

// Reserve capacity
map.try_reserve(100).expect("Failed to allocate");
assert!(map.capacity() >= 100);

// Populate map
for i in 0..10 {
    map.insert(i, i * 2);
}

// Shrink to fit current size
map.shrink_to_fit();
assert!(map.capacity() >= map.len());

// Check size
assert_eq!(map.len(), 10);
assert!(!map.is_empty());
```

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

### Inserting and Updating Entries in DashMap (Rust)

Source: https://context7.com/xacrimon/dashmap/llms.txt

Covers insertion and update operations for DashMap. It shows basic `insert`, conditional insertion using the `entry` API with `and_modify` and `or_insert`, and lazy initialization with `or_insert_with`.

```rust
use dashmap::DashMap;

let map = DashMap::new();

// Basic insert - returns old value if key existed
let old = map.insert("name", "Alice");
assert_eq!(old, None);

let old = map.insert("name", "Bob");
assert_eq!(old, Some("Alice"));

// Entry API for conditional insertion
map.entry("counter")
    .and_modify(|v| *v += 1)
    .or_insert(0);

// or_insert returns mutable reference to value
let mut ref_mut = map.entry("score").or_insert(100);
*ref_mut += 50;
assert_eq!(*map.get("score").unwrap(), 150);

// or_insert_with for lazy initialization
map.entry("expensive")
    .or_insert_with(|| {
        // Only computed if key doesn't exist
        expensive_computation()
    });

fn expensive_computation() -> i32 { 42 }
```

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

### DashSet: Concurrent HashSet Operations and Thread Safety

Source: https://context7.com/xacrimon/dashmap/llms.txt

Illustrates the usage of DashSet, a concurrent HashSet, focusing on thread-safe insertions, set operations like contains and remove, and iteration. It shows how to use `Arc` to share the DashSet across multiple threads for concurrent access.

```rust
use dashmap::DashSet;
use std::sync::Arc;
use std::thread;

// Create concurrent set
let set = Arc::new(DashSet::new());

// Spawn threads to insert values
let handles: Vec<_> = (0..4)
    .map(|i| {
        let set = Arc::clone(&set);
        thread::spawn(move || {
            for j in 0..25 {
                set.insert(i * 25 + j);
            }
        })
    })
    .collect();

for handle in handles {
    handle.join().unwrap();
}

// Set operations
assert_eq!(set.len(), 100);
assert!(set.contains(&50));

// Insert returns false if already present
assert!(!set.insert(50));
assert!(set.insert(200));

// Remove from set
let removed = set.remove(&50);
assert_eq!(removed, Some(50));

// Iteration
for item in set.iter() {
    println!("{}", *item);
}

// Retain matching items
set.retain(|&value| value < 100);
assert_eq!(set.len(), 99); // 0-99 minus the removed 50
```

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

### DashMap Thread-Safe Counter Pattern

Source: https://context7.com/xacrimon/dashmap/llms.txt

Demonstrates a common pattern for implementing thread-safe counters using DashMap. Multiple threads concurrently increment counters identified by keys, ensuring data integrity without explicit locking.

```rust
use dashmap::DashMap;
use std::sync::Arc;
use std::thread;

let counters = Arc::new(DashMap::new());

// Spawn multiple threads incrementing various counters
let handles: Vec<_> = (0..10)
    .map(|thread_id| {
        let counters = Arc::clone(&counters);
        thread::spawn(move || {
            for i in 0..100 {
                let counter_key = i % 5; // 5 different counters
                counters
                    .entry(counter_key)
                    .and_modify(|count| *count += 1)
                    .or_insert(1);
            }
        })
    })
    .collect();

for handle in handles {
    handle.join().unwrap();
}

// Each counter should have been incremented 200 times (10 threads * 100 / 5)
for i in 0..5 {
    assert_eq!(*counters.get(&i).unwrap(), 200);
}

println!("All counters: {:?}", counters);
```

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

### DashMap Bulk Operations: Retain, Alter, and Clear Entries

Source: https://context7.com/xacrimon/dashmap/llms.txt

Covers bulk operations in DashMap, including retaining elements based on a predicate, altering specific values, modifying all values, and clearing the map. It also shows how to view an entry's value without holding a lock.

```rust
use dashmap::DashMap;

let map = DashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

// Retain only matching elements
map.retain(|key, value| *value > 1);
assert_eq!(map.len(), 2);
assert!(!map.contains_key("a"));

// Alter specific value
map.insert("x", 10);
map.alter("x", |_key, value| value * 2);
assert_eq!(*map.get("x").unwrap(), 20);

// Alter all values
map.alter_all(|_key, value| value + 100);
assert_eq!(*map.get("b").unwrap(), 102);
assert_eq!(*map.get("c").unwrap(), 103);

// View without holding lock
let is_even = map.view("x", |_key, value| value % 2 == 0);
assert_eq!(is_even, Some(true));

// Clear all entries
map.clear();
assert!(map.is_empty());
```

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

### DashMap Read-Only View: Efficient Concurrent Read Access

Source: https://context7.com/xacrimon/dashmap/llms.txt

Explains how to convert a DashMap into a read-only view for efficient, lock-free read access. This is useful when sharing data across threads where mutations are infrequent or non-existent.

```rust
use dashmap::DashMap;
use std::sync::Arc;
use std::thread;

// Create and populate map
let map = DashMap::new();
map.insert("config", "production");
map.insert("port", "8080");

// Convert to read-only view for efficient read-only access
let readonly = map.into_read_only();

// Get raw references without locking overhead
let config: &str = readonly.get("config").unwrap();
assert_eq!(config, "production");

// Share read-only view across threads
let view = Arc::new(readonly);
let handles: Vec<_> = (0..10)
    .map(|_| {
        let view = Arc::clone(&view);
        thread::spawn(move || {
            if let Some(port) = view.get("port") {
                println!("Port: {}", port);
            }
        })
    })
    .collect();

for handle in handles {
    handle.join().unwrap();
}

// Iterate with raw references
for (key, value) in view.iter() {
    println!("{}: {}", key, value);
}

// Convert back to mutable DashMap if needed
let map_again = Arc::try_unwrap(view).unwrap().into_inner();
map_again.insert("new_key", "new_value");
```

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

### Removing Entries from DashMap (Rust)

Source: https://context7.com/xacrimon/dashmap/llms.txt

Details the various methods for removing entries from a DashMap. Covers basic removal (`remove`), conditional removal based on key-value pairs (`remove_if`), and mutable conditional removal (`remove_if_mut`).

```rust
use dashmap::DashMap;

let map = DashMap::new();
map.insert("Alice", 30);
map.insert("Bob", 25);

// Basic removal - returns key-value pair
if let Some((key, value)) = map.remove("Alice") {
    assert_eq!(key, "Alice");
    assert_eq!(value, 30);
}

// Conditional removal
map.insert("Charlie", 35);
map.remove_if("Charlie", |_key, &value| value > 30);
assert!(!map.contains_key("Charlie"));

map.insert("Diana", 28);
map.remove_if("Diana", |_key, &value| value > 50);
assert!(map.contains_key("Diana")); // Not removed

// Mutable conditional removal
map.remove_if_mut("Diana", |_key, value| {
    if *value < 30 {
        *value += 10; // Can modify before deciding
        false // Don't remove
    } else {
        true
    }
});
assert_eq!(*map.get("Diana").unwrap(), 38);
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.