Uses old Rust 2015
0.8.0 |
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#51 in #memoization
35KB
648 lines
Near fork of https://github.com/jaemk/cached crate with some optimizations.
lib.rs
:
Caching structures and simplified function memoization
cached
provides implementations of several caching structures as well as a handy macro
for defining memoized functions.
Memoized functions defined using cached!
macros are thread-safe with the backing function-cache wrapped in mutex.
The function-cache is not locked for the duration of the function's execution, so initial (on an empty cache)
concurrent calls of long-running functions with the same arguments will each execute fully and each overwrite
the memoized value as they complete. This mirrors the behavior of Python's functools.lru_cache
.
See cached::stores
docs for details about the
cache stores available.
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!cached!
functions cannot live directly underimpl
blocks sincecached!
expands to aonce_cell
initialization and a funtion definition.
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;
/// Defines a function named `fib` that uses a cache named `FIB`
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.
The following example uses a SizedCache
(LRU):
#[macro_use] extern crate cached;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
/// Defines a function `compute` that uses an LRU cache named `COMPUTE` which has a
/// size limit of 50 items. The `cached!` macro will implicitly combine
/// the function arguments into a tuple to be used as the cache key.
cached!{
COMPUTE: SizedCache<(u64, u64), u64> = SizedCache::with_size(50);
fn compute(a: u64, b: u64) -> u64 = {
sleep(Duration::new(2, 0));
return a * b;
}
}
3.) The cached_key
macro functions identically, but allows you to define the
cache key as an expression.
#[macro_use] extern crate cached;
use std::thread::sleep;
use std::time::Duration;
use cached::SizedCache;
/// Defines a function named `length` that uses an LRU cache named `LENGTH`.
/// The `Key = ` expression is used to explicitly define the value that
/// should be used as the cache key. Here the borrowed arguments are converted
/// to an owned string that can be stored in the global function cache.
cached_key!{
LENGTH: SizedCache<String, usize> = SizedCache::with_size(50);
Key = { format!("{}{}", a, b) };
fn length(a: &str, b: &str) -> usize = {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}
}
4.) The cached_result
and cached_key_result
macros function similarly to cached
and cached_key
respectively but the cached function needs to return Result
(or some type alias like io::Result
). If the function returns Ok(val)
then val
is cached, but errors are not. Note that only the success type needs to implement
Clone
, not the error type. When using cached_result
and cached_key_result
,
the cache type cannot be derived and must always be explicitly specified.
#[macro_use] extern crate cached;
use cached::UnboundCache;
/// Cache the successes of a function.
/// To use `cached_key_result` add a key function as in `cached_key`.
cached_result!{
MULT: UnboundCache<(u64, u64), u64> = UnboundCache::new(); // Type must always be specified
fn mult(a: u64, b: u64) -> Result<u64, ()> = {
if a == 0 || b == 0 {
return Err(());
} else {
return Ok(a * b);
}
}
}
Syntax
The common 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
).
Fine grained control using cached_control!
The cached_control!
macro allows you to provide expressions that get plugged into key areas
of the memoized function. While the cached
and cached_result
variants are adequate for most
scenarios, it can be useful to have the ability to customize the macro's functionality.
#[macro_use] extern crate cached;
use cached::UnboundCache;
/// The following usage plugs in expressions to make the macro behave like
/// the `cached_result!` macro.
cached_control!{
CACHE: UnboundCache<String, String> = UnboundCache::new();
// Use an owned copy of the argument `input` as the cache key
Key = { input.to_owned() };
// If a cached value exists, it will bind to `cached_val` and
// a `Result` will be returned containing a copy of the cached
// evaluated body. This will return before the function body
// is executed.
PostGet(cached_val) = { return Ok(cached_val.clone()) };
// The result of executing the function body will be bound to
// `body_result`. In this case, the function body returns a `Result`.
// We match on the `Result`, returning an early `Err` if the function errored.
// Otherwise, we pass on the function's result to be cached.
PostExec(body_result) = {
match body_result {
Ok(v) => v,
Err(e) => return Err(e),
}
};
// When inserting the value into the cache we bind
// the to-be-set-value to `set_value` and give back a copy
// of it to be inserted into the cache
Set(set_value) = { set_value.clone() };
// Before returning, print the value that will be returned
Return(return_value) = {
println!("{}", return_value);
Ok(return_value)
};
fn can_fail(input: &str) -> Result<String, String> = {
let len = input.len();
if len < 3 { Ok(format!("{}-{}", input, len)) }
else { Err("too big".to_string()) }
}
}
Dependencies
~1.5MB
~24K SLoC