LazyUpdate::exec uses a &mut ref?

[juliusl]

Description

LazyUpdate has two exec fn's, exec and exec_mut. However it looks like their function signatures are identical?

specs/src/world/lazy.rs

Lines 303 to 305 in 81073f3

	pub fn exec<F>(&self, f: F)
	where
	F: FnOnce(&mut World) + 'static,

specs/src/world/lazy.rs

Lines 337 to 339 in 81073f3

	pub fn exec_mut<F>(&self, f: F)
	where
	F: FnOnce(&mut World) + 'static,

I was wondering what is the difference between the two?

[Imberflur]

looks like they became the same in b4e83ce

I don't see any reason to have a &World variant here so they can probably be merged into a single method.