[−][src]Crate easy_ext
An attribute macro for easily writing extension trait pattern.
Examples
use easy_ext::ext; #[ext(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) } }
Code like this will be generated:
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.
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 as the first argument to the #[ext]
attribute. For example:
use easy_ext::ext; // unnamed #[ext(pub)] impl str { fn foo(&self) {} } // named #[ext(pub StrExt)] 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
:
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
If you want the extension trait to be a subtrait of another trait,
add Self: SubTrait
bound to the where
clause.
use easy_ext::ext; #[ext(Ext)] impl<T> T where Self: Default, { fn method(&self) {} }
Supported items
Associated functions (methods)
use easy_ext::ext; #[ext(Ext)] impl<T> T { fn method(&self) {} }
Associated constants
use easy_ext::ext; #[ext(Ext)] impl<T> T { const MSG: &'static str = "Hello!"; }
Attribute Macros
ext | An attribute macro for easily writing extension trait pattern. |