Higher-Rank Trait Bounds (HRTB)

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Higher-Rank Trait Bounds (HRTB)

Higher-Rank Trait Bounds (HRTB) allow you to specify that a bound holds for all possible lifetimes. The 'for<'a>' syntax ensures the closure can handle a reference with any lifetime, rather than a specific one fixed at the call site.

snippet.rs
rust
fn process_data<F>(data: &str, handler: F)
where
    F: for<'a> Fn(&'a str),
{
    handler(data);
}
 
fn main() {
    process_data("expert", |s| println!("Processing: {}", s));
}

Breakdown

for<'a> Fn(&'a str)

Specifies that the function F must implement the Fn trait for any lifetime 'a.

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Higher-Rank Trait Bounds (HRTB)

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