Preconditions

Preconditions are some conditions that are checked prior to the function-body execution.

They can be applied at the function-level only, and are constructed through the use of the pre keyword. If we want our precondition check to persist into release builds, we would use the guarded keyword prior to pre.

So a regular, non-release build persistent precondition would happen at runtime (or compile-time where possible):

fn some_function(x: i32) bool = {
    pre {
        x > 0
    }
    return true
}

And a release-build persistent precondition would be defined like so:

fn some_other_function(x: usize) void = {
    guarded pre {
        x > 20
    }
    do_some_other_thing()
}