Return types

1. To make sure that the method returns the type that you want

For example:

The return type follows the type grammar.

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

1. Making sure a method returns nil without needing to add an extra nil at the end, or at every return point

These methods usually imply a side effect.

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

NoReturn return type

Some expressions won’t return to the current scope and therefore have no return type. This is expressed as the special return type .

This is for example useful for deconstructing union types:

The compiler recognizes that in case string is , the right hand side of the expression string || raise will be evaluated. Since typeof(raise "Empty input") is NoReturn the execution would not return to the current scope in that case. That leaves only String as resulting type of the expression.

Every expression whose code paths all result in NoReturn will be NoReturn as well. does not show up in a union type because it would essentially be included in every expression’s type. It is only used when an expression will never return to the current scope.