Why bother writing similar code twice for blocking and async code?
When implementing both sync and async versions of API in a crate, most API of the two version are almost the same except for some async/await keyword.
maybe-async-cfg help unifying async and sync implementation by procedural macro.
- Write async code with normal async, await, and let maybe_async_cfg handles those async
and await when you need a blocking code.
- Add maybe attributes and specify feature-based conditions under which sync or async code
should be generated.
- Use only_if (or remove_if) to keep code in specified version if necessary.
The maybe procedural macro can be applied to the following codes:
- use declaration
- trait declaration
- trait implementation
- function definition
- struct and enum definition
RECOMMENDATION: Enable resolver ver2 in your crate, which is introduced in Rust 1.51. If not, two crates in dependency with conflict version (one async and another blocking) can fail complilation.
The async/await language feature alters the async world of rust. Comparing with the map/and_then style, now the async code really resembles sync version code.
In many crates, the async and sync version of crates shares the same API, but the minor difference that all async code must be awaited prevent the unification of async and sync code. In other words, we are forced to write an async and an sync implementation repectively.
To use maybe-async-cfg, we must know which block of codes is only used on sync implementation,
and which on async. These two versions of the implementation should share the same function
signatures except for async/await keywords.
Use maybe macro for code that is the same in both async and sync versions except for
async/await keywords. Specify in the macro parameters the conditions (based on features) under
which async and/or sync versions of the code should appear.
attribute macro maybe
Offers a unified way to provide sync and async conversion on demand depending on features, enabled for your crate, with async first policy.
```toml [dependencies] maybeasynccfg = "0.2"
[features] usesync = [] useasync = [] ```
In this and all the following examples, we use two features. But you can use any conditions
that are convenient for you, for example, replacing feature="use_sync" with
not(feature="use_async") everywhere. Feel free, maybe-async-cfg does not analyze the
conditions in any way, just substituting them as is.
Add the maybe attribute before all the items that need to be changed in different versions
of the code (sync or async).
Want to keep async code? Specify the async parameter with the condition (based on
features) when your code should be async.
Wanna convert async code to sync? Specify the sync parameter with the condition when the
sync code should be generated.
```rust, no_run
idents(Foo),
sync(feature="use_sync"),
async(feature="use_async")
)] struct Struct { f: Foo, }
After convertation:
rust, no_run
struct StructSync { f: FooSync, }
struct StructAsync { f: FooAsync, } ```
procedural macro content
The content macro allows you to specify common parameters for many maybe macros. Use the
internal default attribute with the required parameters inside the content macro.
```rust, norun maybeasync_cfg::content!{
idents(Foo, Bar),
)]
struct Struct { f: Foo, }
async fn func(b: Bar) {
todo!()
}
} // content!
After convertation:
rust, no_run
struct StructSync { f: FooSync, }
struct StructAsync { f: FooAsync, }
fn func_sync(b: BarSync) { todo!() }
async fn func_async(b: BarAsync) { todo!() } ```
When implementing rust client for any services, like awz3. The higher level API of async and sync version is almost the same, such as creating or deleting a bucket, retrieving an object and etc.
The example service_client is a proof of concept that maybe_async_cfg can actually free us
from writing almost the same code for sync and async. We can toggle between a sync AWZ3 client
and async one by is_sync feature gate when we add maybe-async-cfg to dependency.
This crate is a redesigned fork of these wonderful crates:
Thanks!
MIT