ptth/crates/always_equal/README.md

Always-Equal

Always-Equal lets you wrap PartialEq implementations around things that cannot be compared, like a File.

To use Always-Equal, put these two conditional use statements in your module:

#[cfg (test)]
use always_equal::test::AlwaysEqual;

#[cfg (not (test))]
use always_equal::prod::AlwaysEqual;

Then wrap AlwaysEqual around anything that needs PartialEq but can't possibly implement it:

use std::fs::File;
use always_equal::test::AlwaysEqual;

#[derive (Debug, PartialEq)]
pub struct MyStruct {
	pub b: bool,
	pub i: i64,
	pub file: AlwaysEqual <File>,
}

// In test code, you can create an empty wrapper using
// `testing_blank`, which is equal to any other wrapper:

let expected = MyStruct {
	b: true,
	i: 0,
	file: AlwaysEqual::testing_blank (),
};

# let my_file = File::open ("Cargo.toml").unwrap ();
let actual = MyStruct {
	b: true,
	i: 0,
	file: my_file.into (),
};

assert_eq! (expected, actual);

This is implemented with Option in test mode. In production mode, wrappers are never equal to any other wrapper, and the Option is removed so that sizeof::<AlwaysEqual <T>> () == sizeof::<T> should be true.