dataloader 0.7.0

Rust implementation of Facebook's DataLoader using futures.
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# Dataloader

[![Build Status](https://travis-ci.org/cksac/dataloader-rs.svg?branch=master)](https://travis-ci.org/cksac/dataloader-rs)
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Rust implementation of [Facebook's DataLoader](https://github.com/facebook/dataloader) using [futures](https://docs.rs/futures-preview).

[Documentation](https://docs.rs/dataloader)

## Features

* [x] Batching load requests
* [x] Caching load results

## Usage

Add to your `Cargo.toml`:
```toml
[dependencies]
dataloader = "0.6.0"
futures = "0.3"
```

Add to your crate:
```rust
use dataloader::{BatchFn, BatchFuture, Loader};
use futures::{executor, future, FutureExt as _, TryFutureExt as _};

struct Batcher;

impl BatchFn<i32, i32> for Batcher {
    type Error = ();

    fn load(&self, keys: &[i32]) -> BatchFuture<i32, Self::Error> {
        println!("load batch {:?}", keys);
        future::ready(keys.into_iter().map(|v| v * 10).collect())
            .unit_error()
            .boxed()
    }
}

fn main() {
    let mut rt = executor::LocalPool::new();

    let loader = Loader::new(Batcher);
    println!("\n -- Using Loader --");
    {
        let v1 = loader
            .load(3)
            .and_then(|v| loader.load_many(vec![v, v + 5, v + 10]));
        let v2 = loader
            .load(4)
            .and_then(|v| loader.load_many(vec![v, v + 5, v + 10]));
        let output = rt.run_until(future::try_join(v1, v2)).unwrap();
        let expected = (vec![300, 350, 400], vec![400, 450, 500]);
        assert_eq!(expected, output);
    }

    let ld = loader.cached();
    println!("\n -- Using Cached Loader --");
    {
        let v1 = ld
            .load(3)
            .and_then(|v| ld.load_many(vec![v, v + 5, v + 10]));
        let v2 = ld
            .load(4)
            .and_then(|v| ld.load_many(vec![v, v + 5, v + 10]));
        let output = rt.run_until(future::try_join(v1, v2)).unwrap();
        let expected = (vec![300, 350, 400], vec![400, 450, 500]);
        assert_eq!(expected, output);
    }
}
```

For using with [Tokio](https://docs.rs/tokio) checkout [Tokio example](examples/tokio.rs).