static_str_ops

The static_str_ops crate solves a longstanding issue about how to perform non-const string operations, e.g., format!(), concat!(), etc. and return static string, i.e., &'static str.

Internally, the crate uses a global static HashSet to store all the static strings, and return the reference to the string in the HashSet if the string has been staticized before.

Note

With this crate, the staticized strings will leaked and the reference is hold by the underlying HashSet. The destaticize() method can be used to released the previously added strings.

APIs

This create provides the following macros and functions:

• staticize(s: &str) -> &'static str

  Convert a string to a static string. If the string has been staticized before, return the reference to the string in the HashSet. This function is the most basic usage of this crate, e.g.,

  Examples:

  use static_str_ops::staticize;
  let s: &'static str = staticize(&String::from("hello world!"));

• is_staticized(s: &str) -> bool

  Check if a string has been staticized before.

  Examples:

  let s: &'static str = staticize(&String::from("hello world!"));
  assert!(is_staticized(s));

• destaticize(s: &str) -> bool

  Remove a string from the HashSet. Return true if the string was present and is successfully removed, false otherwise.

  Examples:

  let s: &'static str = staticize(&String::from("hello world!"));
  assert!(destaticize(s));

• static_concat!(s1: expr, s2: expr, ...) -> &'static str

  Concatenate multiple strings into a static string. The arguments can be either a string literal. Like concat!(), but returns a static string.

  Examples:

  let hello_world: &'static str = static_concat!("Hello", ", ", "world!");

• static_format!(s: expr, ...) -> &'static str

  Format a string into a static string. The arguments can be whatever the builtin macro format!() can accept. Like format!(), but returns a static string.

  let name = "John";
  let age = 30;
  let message = static_format!("My name is {} and I'm {} years old.", name, age);

• staticize_once!(expr: expr) -> &'static str

  Similar to staticize(), but the expr will be evaluated only once. Under the hood, std::sync::Once is used.

  Examples:

  let s: &'static str = staticize_once!({
      let s = "";  // can be some expensive computation
      s
  });

  The function will be useful if you have a function that want to return a static string, while the generate logic is non-trivial, and you want this process only happen once, e.g.,

  use static_str_ops::*;
  let make_string = || {
      staticize_once!({
          let s = "";  // can be some expensive computation
          s
      })
  };
  
  let s1: &'static str = make_string();
  let s2: &'static str = make_string();

  When you call make_string() for multiple times, the body will be guaranteed to be evaluated only once.

License

This project is licensed under the BSD-3 Clause license (LICENSE or http://opensource.org/licenses/BSD-3-Clause).