Crate cached [−] [src]
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 thecached_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
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.
#[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):
#[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.
#[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:
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 astatic ref
to the cacheCacheType
is the full type of the cacheCacheInstance
is any expression that yields an instance ofCacheType
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 tokensKey =
, 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 tofunc_name
. Note, the function body can make recursive calls to its cached-self (func_name
).
Reexports
pub use stores::UnboundCache; |
pub use stores::SizedCache; |
pub use stores::TimedCache; |
Modules
macros |
Macro for defining functions that wrap a static-ref cache object. |
stores |
Implementation of various caches |
Macros
cached | |
cached_key |
Traits
Cached |
Cache operations |