Warning

This post was published 108 days ago. The information described in this article may have changed.

Info

This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Passing LazyLock into generic functions (AsRef, Into)

Hi folks,

Recently I played with LazyLock to cache a custom struct with values that can't be const/static and I found that I can't pass LazyLock into a function that uses AsRef<mystruct> instead of simply &mystruct.

(in the example I simply use String instead of a custom struct)

use std::sync::LazyLock;

static CACHED_VALUE: LazyLock<String> = LazyLock::new(|| "This is the cached value".to_owned());

pub fn try_this() {
    let value_not_cached = String::from("abc");
    print_length(value_not_cached); // works ok
    print_length(CACHED_VALUE); // the trait bound LazyLock<std::string::String>: AsRef<str> is not satisfied the trait AsRef<str> is not implemented for LazyLock<std::string::String
}

// stupid example of a function that takes AsRef
pub fn print_length<S>(str: S)
where
    S: AsRef<str>,
{
    let number = str.as_ref().len();
    println!("length is: {number}")
}

This makes sense but I wonder, is there a solution without re-writing functions like print_length that take AsRef<mystruct> or Into<mystruct>.

Thank you.

1 post - 1 participant

Read full topic

🏷️ rust_feed