Version: 1.1.0

Parameterized declarations

A parameterized declaration is a function or struct that works for a family of types. Constraints tell the compiler what that family must support.

Essentials

• Put parameters in brackets and arguments in parentheses.
• Constrain a type parameter with a trait.
• where clauses add boolean conditions on parameters.
• The body can only use operations the constraints promise.
• Call sites infer parameters when the arguments make them obvious.

Example

fn first[T: Movable](items: List[T]) -> T:
    return items[0]

def main():
    var nums = List[Int](4, 5, 6)
    print(first(nums))

Keep in mind

If inference fails, pass the parameter explicitly. The error usually means two types could fit.