Return types

A method's return type is always inferred by the compiler. However, you might want to specify it for two reasons:

  1. To make sure that the method returns the type that you want
  2. To make it appear in documentation comments

For example:

def some_method : String
  "hello"
end

The return type follows the type grammar.

Nil return type

Marking a method as returning Nil will make it return nil regardless of what it actually returns:

def some_method : Nil
  1 + 2
end

some_method # => nil

This is useful for two reasons:

  1. Making sure a method returns nil without needing to add an extra nil at the end, or at every return point
  2. Documenting that the method's return value is of no interest

These methods usually imply a side effect.

Using Void is the same, but Nil is more idiomatic: Void is preferred in C bindings.

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