Need a mechanism to write rust-version-specific code #3795
Description
Since rust is still going through active development, it's hard to write a library that works for both rust-0.4 and rust-incoming. We need a cfg #[cfg(rust_version="0.5")] to carve off chunks of code that have evolved in between versions.
If we want to get more fancy with these controls, I do have an old semantic version parser I wrote back in the 0.3 days. Maybe we could use something like that to let us write checks like:
#[cfg(rust_version=">=0.4-beta")]
#[cfg(rust_version="<=0.4")]
fn foo() { ... }
#[cfg(rust_version=">0.5")]
fn foo() { ... }