# macro_state
 
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.
## Functionality
The `write_state!` macro stores 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`, 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")` - write "value" as the value for the key "key"
* `read_state!("key")` - returns the value for the key "key", panicking 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
Non-macro analogue functions (`proc_write_state`, `proc_read_state`, etc) are provided for all
of the above macros. Note that these non-macro analogues should _only_ be called from within
proc macros. They will not work if you use them outside of proc macro land!
## Installation
First add `macro_state` as a dependency in your `Cargo.toml` file:
```toml
[dependencies]
macro_state = "0.1.6"
```
Next import the macro:
```rust
#[macro_use]
extern crate macro_state;
```
## Usage
Now you can call `write_state!` and `read_state!` anywhere in your crate, including inside of
proc macros!
```rust
write_state!("top of module", "value 1");
#[test]
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.