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# easy-ext
[](https://crates.io/crates/easy-ext)
[](https://docs.rs/easy-ext)
[](#license)
[](https://www.rust-lang.org)
[](https://github.com/taiki-e/easy-ext/actions)
<!-- tidy:crate-doc:start -->
A lightweight attribute macro for easily writing [extension trait pattern][rfc0445].
```toml
[dependencies]
easy-ext = "1"
```
## Examples
```rust
use easy_ext::ext;
#[ext(ResultExt)]
pub impl<T, E> Result<T, E> {
fn err_into<U>(self) -> Result<T, U>
where
E: Into<U>,
{
self.map_err(Into::into)
}
}
```
Code like this will be generated:
```rust
pub trait ResultExt<T, E> {
fn err_into<U>(self) -> Result<T, U>
where
E: Into<U>;
}
impl<T, E> ResultExt<T, E> for Result<T, E> {
fn err_into<U>(self) -> Result<T, U>
where
E: Into<U>,
{
self.map_err(Into::into)
}
}
```
You can elide the trait name.
```rust
use easy_ext::ext;
#[ext]
impl<T, E> Result<T, E> {
fn err_into<U>(self) -> Result<T, U>
where
E: Into<U>,
{
self.map_err(Into::into)
}
}
```
Note that in this case, `#[ext]` assigns a random name, so you cannot
import/export the generated trait.
### Visibility
There are two ways to specify visibility.
#### Impl-level visibility
The first way is to specify visibility at the impl level. For example:
```rust
use easy_ext::ext;
// unnamed
#[ext]
pub impl str {
fn foo(&self) {}
}
// named
#[ext(StrExt)]
pub impl str {
fn bar(&self) {}
}
```
#### Associated-item-level visibility
Another way is to specify visibility at the associated item level.
For example, if the method is `pub` then the trait will also be `pub`:
```rust
use easy_ext::ext;
#[ext(ResultExt)] // generate `pub trait ResultExt`
impl<T, E> Result<T, E> {
pub fn err_into<U>(self) -> Result<T, U>
where
E: Into<U>,
{
self.map_err(Into::into)
}
}
```
This is useful when migrate from an inherent impl to an extension trait.
Note that the visibility of all the associated items in the `impl` must be identical.
Note that you cannot specify impl-level visibility and associated-item-level visibility at the same time.
### [Supertraits](https://doc.rust-lang.org/reference/items/traits.html#supertraits)
If you want the extension trait to be a subtrait of another trait,
add `Self: SubTrait` bound to the `where` clause.
```rust
use easy_ext::ext;
#[ext(Ext)]
impl<T> T
where
Self: Default,
{
fn method(&self) {}
}
```
### Supported items
#### [Associated functions (methods)](https://doc.rust-lang.org/reference/items/associated-items.html#associated-functions-and-methods)
```rust
use easy_ext::ext;
#[ext]
impl<T> T {
fn method(&self) {}
}
```
#### [Associated constants](https://doc.rust-lang.org/reference/items/associated-items.html#associated-constants)
```rust
use easy_ext::ext;
#[ext]
impl<T> T {
const MSG: &'static str = "Hello!";
}
```
#### [Associated types](https://doc.rust-lang.org/reference/items/associated-items.html#associated-types)
```rust
use easy_ext::ext;
#[ext]
impl str {
type Owned = String;
fn method(&self) -> Self::Owned {
self.to_owned()
}
}
```
[rfc0445]: https://github.com/rust-lang/rfcs/blob/HEAD/text/0445-extension-trait-conventions.md
<!-- tidy:crate-doc:end -->
## License
Licensed under either of [Apache License, Version 2.0](LICENSE-APACHE) or
[MIT license](LICENSE-MIT) at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.
|
