singleton-registry

A thread-safe singleton registry for Rust.
Store and retrieve any type globally - structs, primitives, functions, or closures.
Each type can have only one instance registered at a time (true singleton pattern).
Designed for write-once, read-many pattern with zero-cost abstractions.

Features

Thread-safe: All operations are safe to use across multiple threads
Type-safe: Values are stored and retrieved with full type information
True singleton: Only one instance per type - later registrations override previous ones
Zero-cost abstractions: Minimal runtime overhead
Tracing support: Optional callback system for monitoring registry operations
No external dependencies: Pure Rust implementation

Quick Start

use singleton_registry::{register, get};
use std::sync::Arc;

// Register a value (only one String can be registered)
register("Hello, World!".to_string());

// Later registration of same type overrides the previous one
register("New message!".to_string());

// Retrieve the latest value
let message: Arc<String> = get().unwrap();
assert_eq!(&*message, "New message!");

Advanced Usage

use singleton_registry::{register, get, contains, set_trace_callback};
use std::sync::Arc;

// Register different types
register(42i32);
register("config".to_string());

// Register a function pointer
let multiply_by_two: fn(i32) -> i32 = |x| x * 2;
register(multiply_by_two);

// Check if a type is registered
assert!(contains::<i32>().unwrap());

// Retrieve values
let number: Arc<i32> = get().unwrap();
let config: Arc<String> = get().unwrap();
let doubler: Arc<fn(i32) -> i32> = get().unwrap();

// Use the function
let result = doubler(21); // returns 42

// Set up tracing
set_trace_callback(|event| {
    println!("Registry event: {}", event);
});

API Reference

register(value) - Register a value in the global registry
register_arc(arc_value) - Register an Arc-wrapped value (more efficient)
get::<T>() - Retrieve a value as Arc<T>
get_cloned::<T>() - Retrieve a cloned value (requires Clone)
contains::<T>() - Check if a type is registered
set_trace_callback(callback) - Set up tracing for registry operations
clear_trace_callback() - Disable tracing

Use Cases

Application singletons (Config, Logger, DatabasePool, etc.)
Global variables and constants shared across modules
Function helpers and utility closures accessible anywhere
Service location for shared components
Cross-cutting concerns shared across modules

Design Philosophy

Simple: Clean API without complex macros or derive attributes
Safe: Values stored in Arc<T> with full type checking
Global: One central registry shared across the entire program
Singleton: Each type can only have one registered instance - true singleton behavior
Override-friendly: Later registrations replace previous ones for the same type
Efficient: Write-once, read-many pattern optimized for performance

Installation

Add this to your Cargo.toml:

[dependencies]
singleton-registry = "1.0"

License

BSD-3-Clause

singleton-registry 1.0.0