# cached

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> Caching structures and simplified function memoization

`cached` provides implementations of several caching structures as well as a handy macros
for defining memoized functions.

Memoized functions defined using [`#[cached]`](proc_macro::cached)/[`#[once]`](proc_macro::once)/[`#[io_cached]`](proc_macro::io_cached)/[`cached!`](crate::macros) macros are thread-safe with the backing
function-cache wrapped in a mutex/rwlock, or externally synchronized in the case of `#[io_cached]`.
By default, 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`. To synchronize the execution and caching
of un-cached arguments, specify `#[cached(sync_writes = true)]` / `#[once(sync_writes = true)]` (not supported by `#[io_cached]`.

- See [`cached::stores` docs](https://docs.rs/cached/latest/cached/stores/index.html) cache stores available.
- See [`proc_macro`](https://docs.rs/cached/latest/cached/proc_macro/index.html) for more procedural macro examples.
- See [`macros`](https://docs.rs/cached/latest/cached/macros/index.html) for more declarative macro examples.

**Features**

- `default`: Include `proc_macro` and `ahash` features
- `proc_macro`: Include proc macros
- `ahash`: Enable the optional `ahash` hasher as default hashing algorithm.
- `async`: Include support for async functions and async cache stores
- `async_tokio_rt_multi_thread`: Enable `tokio`'s optional `rt-multi-thread` feature.
- `redis_store`: Include Redis cache store
- `redis_async_std`: Include async Redis support using `async-std` and `async-std` tls support, implies `redis_store` and `async`
- `redis_tokio`: Include async Redis support using `tokio` and `tokio` tls support, implies `redis_store` and `async`
- `redis_connection_manager`: Enable the optional `connection-manager` feature of `redis`. Any async redis caches created
                              will use a connection manager instead of a `MultiplexedConnection`
- `redis_ahash`: Enable the optional `ahash` feature of `redis`
- `disk_store`: Include disk cache store
- `wasm`: Enable WASM support. Note that this feature is incompatible with `tokio`'s multi-thread
   runtime (`async_tokio_rt_multi_thread`) and all Redis features (`redis_store`, `redis_async_std`, `redis_tokio`, `redis_ahash`)

The procedural macros (`#[cached]`, `#[once]`, `#[io_cached]`) offer more features, including async support.
See the [`proc_macro`](crate::proc_macro) and [`macros`](crate::macros) modules for more samples, and the
[`examples`](https://github.com/jaemk/cached/tree/master/examples) directory for runnable snippets.

Any custom cache that implements `cached::Cached`/`cached::CachedAsync` can be used with the `#[cached]`/`#[once]`/`cached!` macros in place of the built-ins.
Any custom cache that implements `cached::IOCached`/`cached::IOCachedAsync` can be used with the `#[io_cached]` macro.

----

The basic usage looks like:

```rust
use cached::proc_macro::cached;

/// Defines a function named `fib` that uses a cache implicitly named `FIB`.
/// By default, the cache will be the function's name in all caps.
/// The following line is equivalent to #[cached(name = "FIB", unbound)]
#[cached]
fn fib(n: u64) -> u64 {
    if n == 0 || n == 1 { return n }
    fib(n-1) + fib(n-2)
}
```

----

```rust
use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
use cached::SizedCache;

/// Use an explicit cache-type with a custom creation block and custom cache-key generating block
#[cached(
    ty = "SizedCache<String, usize>",
    create = "{ SizedCache::with_size(100) }",
    convert = r#"{ format!("{}{}", a, b) }"#
)]
fn keyed(a: &str, b: &str) -> usize {
    let size = a.len() + b.len();
    sleep(Duration::new(size as u64, 0));
    size
}
```

----

```rust
use cached::proc_macro::once;

/// Only cache the initial function call.
/// Function will be re-executed after the cache
/// expires (according to `time` seconds).
/// When no (or expired) cache, concurrent calls
/// will synchronize (`sync_writes`) so the function
/// is only executed once.
#[once(time=10, option = true, sync_writes = true)]
fn keyed(a: String) -> Option<usize> {
    if a == "a" {
        Some(a.len())
    } else {
        None
    }
}
```

----

```compile_fail
use cached::proc_macro::cached;

/// Cannot use sync_writes and result_fallback together
#[cached(
    result = true,
    time = 1,
    sync_writes = true,
    result_fallback = true
)]
fn doesnt_compile() -> Result<String, ()> {
    Ok("a".to_string())
}
```
----

```rust,no_run,ignore
use cached::proc_macro::io_cached;
use cached::AsyncRedisCache;
use thiserror::Error;

#[derive(Error, Debug, PartialEq, Clone)]
enum ExampleError {
    #[error("error with redis cache `{0}`")]
    RedisError(String),
}

/// Cache the results of an async function in redis. Cache
/// keys will be prefixed with `cache_redis_prefix`.
/// A `map_error` closure must be specified to convert any
/// redis cache errors into the same type of error returned
/// by your function. All `io_cached` functions must return `Result`s.
#[io_cached(
    map_error = r##"|e| ExampleError::RedisError(format!("{:?}", e))"##,
    ty = "AsyncRedisCache<u64, String>",
    create = r##" {
        AsyncRedisCache::new("cached_redis_prefix", 1)
            .set_refresh(true)
            .build()
            .await
            .expect("error building example redis cache")
    } "##
)]
async fn async_cached_sleep_secs(secs: u64) -> Result<String, ExampleError> {
    std::thread::sleep(std::time::Duration::from_secs(secs));
    Ok(secs.to_string())
}
```

----

```rust,no_run,ignore
use cached::proc_macro::io_cached;
use cached::DiskCache;
use thiserror::Error;

#[derive(Error, Debug, PartialEq, Clone)]
enum ExampleError {
    #[error("error with disk cache `{0}`")]
    DiskError(String),
}

/// Cache the results of a function on disk.
/// Cache files will be stored under the system cache dir
/// unless otherwise specified with `disk_dir` or the `create` argument.
/// A `map_error` closure must be specified to convert any
/// disk cache errors into the same type of error returned
/// by your function. All `io_cached` functions must return `Result`s.
#[io_cached(
    map_error = r##"|e| ExampleError::DiskError(format!("{:?}", e))"##,
    disk = true
)]
fn cached_sleep_secs(secs: u64) -> Result<String, ExampleError> {
    std::thread::sleep(std::time::Duration::from_secs(secs));
    Ok(secs.to_string())
}
```


Functions defined via macros will have their results cached using the
function's arguments as a key, a `convert` expression specified on a procedural macros,
or a `Key` block specified on a `cached_key!` declarative macro.

When a macro-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:
  - For all store types, except Redis, must be owned and implement `Clone`
  - For the Redis store type, must be owned and implement `serde::Serialize + serde::DeserializeOwned`
- Function arguments:
  - For all store types, except Redis, must either be owned and implement `Hash + Eq + Clone`,
    the `cached_key!` macro is used with a `Key` block specifying key construction, or
    a `convert` expression is specified on a procedural macro to specify how to construct a key
    of a `Hash + Eq + Clone` type.
  - For the Redis store type, must either be owned and implement `Display`, or the `cached_key!` & `Key`
    or procedural macro & `convert` expression used to specify how to construct a key of a `Display` type.
- Arguments and return values will be `cloned` in the process of insertion and retrieval. Except for Redis
  where arguments are formatted into `Strings` and values are de/serialized.
- Macro-defined functions should not be used to produce side-effectual results!
- Macro-defined functions cannot live directly under `impl` blocks since macros expand to a
  `once_cell` initialization and one or more function definitions.
- Macro-defined functions cannot accept `Self` types as a parameter.



License: MIT