# memoize

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A `#[memoize]` attribute for somewhat simple Rust functions: That is, functions
with one or more `Clone`-able arguments, and a `Clone`-able return type. That's it.

**NEWS**: The crate has been updated so that you don't need to separately import `lru`,
    `lazy_static`, and other dependencies. Now everything should work automatically. Remember to
    enable the `full` feature to use LRU caching and other additional features.

Read the documentation (`cargo doc --open`) for the sparse details, or take a
look at the `examples/`, if you want to know more:

```rust
// From examples/test2.rs

use memoize::memoize;

#[memoize]
fn hello(arg: String, arg2: usize) -> bool {
  arg.len()%2 == arg2
}

fn main() {
  // `hello` is only called once here.
  assert!(! hello("World".to_string(), 0));
  assert!(! hello("World".to_string(), 0));
  // Sometimes one might need the original function.
  assert!(! memoized_original_hello("World".to_string(), 0));
}
```

This is expanded into (with a few simplifications):

```rust
std::thread_local! {
  static MEMOIZED_MAPPING_HELLO : RefCell<HashMap<(String, usize), bool>> = RefCell::new(HashMap::new());
}

pub fn memoized_original_hello(arg: String, arg2: usize) -> bool {
  arg.len() % 2 == arg2
}

#[allow(unused_variables)]
fn hello(arg: String, arg2: usize) -> bool {
  let r = MEMOIZED_MAPPING_HELLO.with(|hm| {
    let mut hm = hm.borrow_mut();
    hm.get(&(arg.clone(), arg2.clone())).cloned()
  });
  if let Some(r) = r {
    return r;
  }

  let r = memoized_original_hello(arg.clone(), arg2.clone());

  MEMOIZED_MAPPING_HELLO.with(|hm| {
    let mut hm = hm.borrow_mut();
    hm.insert((arg, arg2), r.clone());
  });

  r
}

```

## Further Functionality
As can be seen in the above example, each thread has its own cache by default. If you would prefer
that every thread share the same cache, you can specify the `SharedCache` option like below to wrap
the cache in a `std::sync::Mutex`. For example:
```rust
#[memoize(SharedCache)]
fn hello(key: String) -> ComplexStruct {
  // ...
}
```

You can choose to use an [LRU cache](https://crates.io/crates/lru). In fact, if
you know that a memoized function has an unbounded number of different inputs,
you should do this! In that case, use the attribute like this:

```rust
// From examples/test1.rs
// Compile with --features=full
use memoize::memoize;

#[derive(Debug, Clone)]
struct ComplexStruct {
  // ...
}

#[memoize(Capacity: 123)]
fn hello(key: String) -> ComplexStruct {
  // ...
}
```

Adding more caches and configuration options is relatively simple, and a matter
of parsing attribute parameters. Currently, compiling will fail if you use a
parameter such as `Capacity` without the feature `full` being enabled.

Another parameter is TimeToLive, specifying how long a cached value is allowed
to live:

```rust
#[memoize(Capacity: 123, TimeToLive: Duration::from_secs(2))]
```

`chrono::Duration` is also possible, but would have to first be converted to
`std::time::Duration`

```rust
#[memoize(TimeToLive: chrono::Duration::hours(3).to_std().unwrap())]
```

The cached value will never be older than duration provided and instead
recalculated on the next request.

## Contributions

...are always welcome! This being my first procedural-macros crate, I am
grateful for improvements of functionality and style. Please send a pull
request, and don't be discouraged if it takes a while for me to review it; I'm
sometimes a bit slow to catch up here :)   -- Lewin