Keep Calm (and call Clone)

Simple shared types for multi-threaded programs

This library simplifies a number of shared-object patterns that are used in multi-threaded programs such as web-servers. The traditional Rust shared object patterns tend to be somewhat version, for example:

```rust

use std::sync::{Arc, Mutex};

let object = "123".to_string(); let shared = Arc::new(Mutex::new(object)); shared.lock().expect("Mutex was poisoned"); ```

SharedRW

The [SharedRW] object hides the complexity of managing Arc<Mutex<T>> or Arc<RwLock<T>> behind a single interface:

```rust

use keepcalm::*;

let object = "123".tostring(); let shared = SharedRW::new(object); shared.lockread(); ```

By default, a [SharedRW] object uses Arc<RwLock<T>> under the hood, but you can choose the synchronization primitive at construction time. The [SharedRW] object erases the underlying primitive and you can use them interchangeably:

```rust

use keepcalm::*;

fn useshared(shared: SharedRW) { shared.lockread(); }

let shared = SharedRW::new("123".tostring()); useshared(shared); let shared = SharedRW::newwithtype("123".tostring(), Implementation::Mutex); useshared(shared); ```

Managing the poison state of synchronization primitives can be challenging as well. Rust will poison a Mutex or RwLock if you hold a lock while a panic! occurs.

The SharedRW type allows you to specify a [PoisonPolicy] at construction time. By default, if a synchronization primitive is poisoned, the SharedRW will panic! on access. This can be configured so that poisoning is ignored:

```rust

use keepcalm::*;

let shared = SharedRW::newwithpolicy("123".to_string(), PoisonPolicy::Ignore); ```

Shared

The [Shared] object is similar to Rust's [std::sync::Arc], but adds the ability to project.

Projection

Both [Shared] and [SharedRW] allow projection into the underlying type. Projection can be used to select either a subset of a type, or to cast a type to a trait.

Note that projections are always linked to the root object!

Casting:

```rust

use keepcalm::*;

let shared = SharedRW::new("123".tostring()); let sharedasref: SharedRW> = shared.project(project_cast!(x: String => dyn AsRef)); ```

Subset of a struct/tuple:

```rust

use keepcalm::*;

[derive(Default)]

struct Foo { tuple: (String, usize) }

let shared = SharedRW::new(Foo::default()); let shared_string: SharedRW = shared.project(project!(x: Foo, x.tuple.0));

shared_string.lock_write() += "hello, world"; assert_eq!(shared.lock_read().tuple.0, "hello, world"); assert_eq!(sharedstring.lockread(), "hello, world"); ```

Unsized types

Both [Shared] and [SharedRW] support unsized types, but due to current limitations in the language (see [std::ops::CoerceUnsized] for details), you need to construct them in special ways.

Unsized traits are supported, but you will either need to specify Send + Sync in the shared type, or [project_cast!] the object:

```rust

use keepcalm::*;

// In this form, Send + Sync are visible in the shared type let boxed: Box + Send + Sync> = Box::new("123".tostring()); let shared: SharedRW + Send + Sync> = SharedRW::frombox(boxed);

// In this form, Send + Sync are erased via projection let shared = SharedRW::new("123".tostring()); let sharedasref: SharedRW> = shared.project(project_cast!(x: String => dyn AsRef)); ```

Unsized slices are supported using a box:

```rust

use keepcalm::*;

let boxed: Box<[i32]> = Box::new([1, 2, 3]); let shared: SharedRW<[i32]> = SharedRW::from_box(boxed); ```