#proc-macro #state #compile-time #global #key-value #within #calls


A set of macros allowing storing and loading global state at compile-time within proc macros

11 releases

0.2.0 Oct 18, 2022
0.1.9 Oct 13, 2022
0.1.5 Jun 4, 2022
0.1.2 May 30, 2022

#586 in Procedural macros

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crates.io GitHub Workflow Status (branch) docs.rs

Currently, Rust does not provide the ability to keep track of any sort of global state between macro calls out of the box.

This crate contains a series of macros that make it trivial to save and load global state (in the form of string keys and values) at compile time and from within proc macros. State that was set at compile-time can also be read directly by runtime code, if needed.


The write_state! and append_state! macros store state in flat files that live in the target build directory for the current project. This ensures that when you do things like run cargo clean or change your code, the current state values are automatically reset as well. In other words, this crate automatically tracks with the build artifacts of whatever is using it.

After compilation, whatever values were present at compile-time are baked into the resulting binary.


Currently, we offer the following macros:

  • write_state!("key","value") writes "value" as the value for the key "key"
  • read_state!("key") returns the value for the key "key", issuing a compiler error if it can't be found
  • init_state!("key","value") if the key "key" has a value, returns it, otherwise sets it to "value" and also returns it. This can be used to quickly initialize a key value pair that may have existing data
  • has_state!("key") returns a boolean indicating whether a value has been stored for the key "key"
  • clear_state!("key") clears any existing state value for key "key", if it exists
  • append_state!("key","value") appends "value" to the value list for the specified key. Used in conjunction with read_state_vec! to add to and manage lists within state files.
  • read_state_vec!("key") reads the state file for key "key" as a Vec<String>. Used in conjunction with append_state! to manage manage lists within state files.

Within Proc Macros

Non-macro analogues for all of the macros listed above can be found here. These analogues all begin with proc_, such as proc_read_state, and should only be used within proc macros.

Using these functions anywhere but within a proc macro will result in broken/undefined behavior.


First add macro_state as a dependency in your Cargo.toml file:

macro_state = "0.1.9"

Next set up your imports:

extern crate macro_state;
use macro_state::*;


Now you can call write_state! and read_state! anywhere in your crate, including inside of proc macros!

write_state!("top of module", "value 1");

fn test_write_state() {
    write_state!("top of method", "value 2");
    assert_eq!(read_state!("top of module"), "value 1");
    assert_eq!(read_state!("top of method"), "value 2");

After writing a call to write_state, such as write_state!("my key", "my value");, the state you wrote will now be available at the specified key for use by read_state!("my key"); calls further down in your source code. Note that all of this happens at compile-time, so make sure your source code and macro calls are laid out such that your write_state calls will be compiled before your read_state calls.


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