# cached
[](https://travis-ci.org/jaemk/cached)
[](https://crates.io/crates/cached)
[](https://docs.rs/cached)
> Caching structures and simplified function memoization
`cached` provides implementations of several caching structures as well as a handy macro
for defining memoized functions.
## Defining memoized functions using `cached!`
`cached!` defined functions will have their results cached using the function's arguments as a key
(or a specific expression when using `cached_key!`).
When a `cached!` defined function is called, the function's cache is first checked for an already
computed (and still valid) value before evaluating the function body.
Due to the requirements of storing arguments and return values in a global cache:
- Function return types must be owned and implement `Clone`
- Function arguments must either be owned and implement `Hash + Eq + Clone` OR the `cached_key!`
macro must be used to convert arguments into an owned + `Hash + Eq + Clone` type.
- Arguments and return values will be `cloned` in the process of insertion and retrieval.
- `cached!` functions should not be used to produce side-effectual results!
**NOTE**: Any custom cache that implements `cached::Cached` can be used with the `cached` macros in place of the built-ins.
See [`examples`](https://github.com/jaemk/cached/tree/master/examples) for basic usage and
an example of implementing a custom cache-store.
### `cached!` and `cached_key!` Usage & Options:
There are several options depending on how explicit you want to be. See below for a full syntax breakdown.
1.) Using the shorthand will use an unbounded cache.
```rust
#[macro_use] extern crate cached;
#[macro_use] extern crate lazy_static;
cached!{
FIB;
fn fib(n: u64) -> u64 = {
if n == 0 || n == 1 { return n }
fib(n-1) + fib(n-2)
}
}
```
2.) Using the full syntax requires specifying the full cache type and providing
an instance of the cache to use. Note that the cache's key-type is a tuple
of the function argument types. If you would like fine grained control over
the key, you can use the `cached_key!` macro.
For example, a `SizedCache` (LRU):
```rust
#[macro_use] extern crate cached;
#[macro_use] extern crate lazy_static;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
cached!{
FIB: SizedCache<(u64, u64), u64> = SizedCache::with_capacity(50);
fn fib(a: u64, b: u64) -> u64 = {
sleep(Duration::new(2, 0));
return a * b;
}
}
```
3.) The `cached_key` macro functions identically, but allows you define the
cache key as an expression.
```rust
#[macro_use] extern crate cached;
#[macro_use] extern crate lazy_static;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
cached_key!{
FIB: SizedCache<String, usize> = SizedCache::with_capacity(50);
Key = { format!("{}{}", a, b) };
fn fib(a: &str, b: &str) -> usize = {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
}
```
## Syntax
The complete macro syntax is:
```rust
cached_key!{
CACHE_NAME: CacheType = CacheInstance;
Key = KeyExpression;
fn func_name(arg1: arg_type, arg2: arg_type) -> return_type = {
// do stuff like normal
return_type
}
}
```
Where:
- `CACHE_NAME` is the unique name used to hold a `static ref` to the cache
- `CacheType` is the full type of the cache
- `CacheInstance` is any expression that yields an instance of `CacheType` to be used
as the cache-store, followed by `;`
- When using the `cached_key!` macro, the "Key" line must be specified. This line must start with
the literal tokens `Key = `, followed by an expression that evaluates to the key, followed by `;`
- `fn func_name(arg1: arg_type) -> return_type` is the same form as a regular function signature, with the exception
that functions with no return value must be explicitly stated (e.g. `fn func_name(arg: arg_type) -> ()`)
- The expression following `=` is the function body assigned to `func_name`. Note, the function
body can make recursive calls to its cached-self (`func_name`).
License: MIT