# Common Collection Traits

   Documentation (https://docs.rs/cc-traits)
   Crate informations (https://crates.io/crates/cc-traits)
   Repository (https://github.com/timothee-haudebourg/cc-traits)

This crate provide traits to describe common operations available on data structures.
This is particularly useful when building new types on top of generic data structures without relying on the actual implementation of the underlying data structure.

Here is an example of the kind of traits provided by this crate:
```rust
/// Mutable collection where new elements can be inserted.
pub trait Insert: Collection {
    /// The output of the insertion function.
    type Output;

    /// Insert a new element in the collection.
    fn insert(&mut self, element: Self::Item) -> Self::Output;
}
```

## Usage

Such traits can be used to define collections with special properties,
independently of the actual internal data structure.
For instance the following code defines an `Ordered<S>` stack collection,
guarantying the well-sortedness of the elements in the stack.

```rust
use cc_traits::{
    Collection,
    Back,
    PushBack
};

/// Ordered stack.
pub struct Ordered<S> {
    inner: S
}

impl<S> Ordered<S> {
    pub fn new() -> Self where S: Default {
        Ordered {
            inner: S::default()
        }
    }
}

impl<S> Ordered<S> {
    /// Push the given element on the stack iff it is grater or equal
    /// to every other element already in the stack.
    pub fn try_push<T>(&mut self, element: T) -> Result<(), T>
    where
        T: PartialOrd,
        S: Collection<Item=T> + Back + PushBack, // `S` must be a stack providing `back` and `push_back`.
        for<'a> S::ItemRef<'a>: PartialOrd<&'a T> // The reference type must be comparable with other reference types.
    {
        if self.inner.back().map(|back| back <= &element).unwrap_or(true) {
            self.inner.push_back(element);
            Ok(())
        } else {
            Err(element)
        }
    }
}

let mut vec: Ordered<Vec<i32>> = Ordered::new(); // a `Vec` is a stack so it works.

assert!(vec.try_push(1).is_ok());
assert!(vec.try_push(2).is_ok());
assert!(vec.try_push(0).is_err());

use std::collections::VecDeque;
let mut deque: Ordered<VecDeque<i32>> = Ordered::new(); // a `VecDeque` is also a stack.

assert!(deque.try_push(1).is_ok());
assert!(deque.try_push(2).is_ok());
assert!(deque.try_push(0).is_err());
```

## Trait aliases

By enabling the `nightly` you can get access to
some trait alias definitions that can be useful to reduce the
verbosity of your code.
Here is an example of such aliases defining the common interface of stacks:
```rust
pub trait Stack<T> = Collection<Item=T> + Len + Back;
pub trait StackMut<T> = Stack<T> + BackMut + PushBack + PopBack;
```

As of version 0.8.0, those traits are also available without the `nightly`
feature as regular trait definitions.

## Standard library

By default, all the traits defined in this crate are implemented (when relevent)
for the standard library collections.
You can disable it by using the `nostd` feature.

## Foreign implementations

In addition to the standard library,
traits are implemented for
some popular crates if you enable the feature of the same name.
Here are the supported crates:

  - [`slab`](https://crates.io/crates/slab) providing the `Slab` collection.
  - [`smallvec`](https://crates.io/crates/smallvec) providing the `SmallVec` collection.
  - [`serde_json`](https://crates.io/crates/serde_json) providing the `Map<String, Value>` collection for JSON objects.
  - [`ijson`](https://crates.io/crates/ijson) providing the `IObject` and `IArray` collections.

## License

Licensed under either of

 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any
additional terms or conditions.
