Void as a variable type

[SamahParticipant]

This may sound like a strange request, but I have a use case where I want to be able to declare a variable or argument as “Void”, and assign a “Void” value to it. Specifically, it’s a generic class and function that passes its type through to a closure, in which Void is a sensible parameter.

Monkey

[crayon-5cb9e343bb29c107123732 inline="true" ]Class Foo<T> Field value:T Method New() End Method Register<X>:Foo<X>(closure:X(T)) Return New Foo<X>(Lambda:Void() closure(value) End) End End ' registers a closure that has a single Int argument and return type String Local a := New Foo<Int> Local closure := a.Register<String>(Lambda:String(result:Int)) Return "Hello " + result End) a.value = 3 Print(closure()) ' prints "Hello 3" ' registers a closure that has a no arguments and a return type of Float Local b := New Foo<Void> Local closure := b.Register<Float>(Lambda:Float(result:Void)) Return 1.0 End) ' don't need to set b.value since it won't be used Print("World " + closure()) ' prints 1.0

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[crayon-5cb9e343bb29c107123732 inline="true" ]Class Foo<T>   Field value:T     Method New()   End     Method Register<X>:Foo<X>(closure:X(T))     Return New Foo<X>(Lambda:Void()       closure(value)     End)   End End   ' registers a closure that has a single Int argument and return type String Local a := New Foo<Int> Local closure := a.Register<String>(Lambda:String(result:Int))   Return "Hello " + result End) a.value = 3 Print(closure()) ' prints "Hello 3"   ' registers a closure that has a no arguments and a return type of Float Local b := New Foo<Void> Local closure := b.Register<Float>(Lambda:Float(result:Void))   Return 1.0 End) ' don't need to set b.value since it won't be used Print("World " + closure()) ' prints 1.0

[/crayon]

Of course this won’t compile, because you can’t define Foo.value as Void, nor can you define the argument to the closure as Void.

Swift allows you to define variables as Void, but the only valid value is (), an empty tuple, which essentially means “nothing”. Not even nil or Null.

If not, I guess there’ll be a requirement to always have a return type, and exactly one argument. Also, there is method to the madness, and the nested closures are required.

[Author]

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