Attribute Macro extension_method 

#[extension_method]

Creates an “extension” method for a type by implementing a custom trait with a single method. This is a workaround to enable chaining utility functions without modifying the original type. The first parameter of the annotated function will be used as self in the trait method.

If it is a generic type parameter (e.g., T, *const T, &mut T, etc.), the same type parameter and its lifetime (if any) will be used as the trait generics.

If the first parameter type is impl Trait, it will be converted to a generic type parameter with a trait bound.

• To specify a custom name for the generated trait, use trait_name = "MyTraitName"
• To specify a custom name for the generic type parameter for impl Trait, use impl_type_param = "MyT"
• The original function will be preserved by default, use remove_fn = true to remove it

Note: The annotated function cannot be extern, and must have at least one input parameter. The input parameter cannot be of type Self. Example:

use core::ops::Add;

#[extension_method(trait_name = "Double", remove_fn = true)]
pub fn double<T>(val: T) -> T where T: Add<Output = T> + Copy {
    val + val
}

let a = 2;
assert_eq!(a.double(), 4);