I would like to simplify the declaration of the following function:
use regex::Regex;
fn oper<'a, F>(regex: &str, op: F) -> (Regex, Box<dyn Fn(i32, i32) -> i32 + 'a>)
where F: Fn(i32, i32) -> i32 + 'a
{
(Regex::new(regex).unwrap(), Box::new(op))
}
I tried to replace the Fn
trait by F
in the return value, but it raises an error:
fn oper<'a, F>(regex: &str, op: F) -> (Regex, Box<dyn F>)
where F: Fn(i32, i32) -> i32 + 'a
{
(Regex::new(regex).unwrap(), Box::new(op))
}
error[E0404]: expected trait, found type parameter `F`
--> src/lib.rs:5:55
|
5 | fn oper<'a, F>(regex: &str, op: F) -> (Regex, Box<dyn F>)
| ^ help: a trait with a similar name exists: `Fn`
error: aborting due to previous error
How can simplify this declaration to avoid duplication of Fn(i32, i32) -> i32 + 'a
?
You could use this technique . In short, define a new trait that requires Fn(i32, i32) -> i32
and implement it for any type that already implements Fn(i32, i32) -> i32
:
use regex::Regex;
// 1. Create a new trait
pub trait MyFn: Fn(i32, i32) -> i32 {}
// 2. Implement it
impl<T> MyFn for T where T: Fn(i32, i32) -> i32 {}
fn oper<'a, F>(regex: &str, op: F) -> (Regex, Box<dyn MyFn + 'a>)
where F: MyFn + 'a
{
(Regex::new(regex).unwrap(), Box::new(op))
}
Note, however, that this might be less readable than just repeating Fn(i32, i32) -> i32
in the signature of oper
.
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