Hi folks,
I just wanted to take a moment to highlight a new ActionScript language
feature that I recently implemented in Royale's compiler: Function type
expressions. Or perhaps you might call them strict function types.
Basically, instead of using the Function type, like this:
var validate:Function;
You can define the function signature as a type, like this (The syntax is
pretty similar to TypeScript's):
var validate:(input:String)=>Boolean;
And then, the compiler can check for mismatches. The following assignment
will fail:
var validate:(input:String)=>Boolean = function(input:ByteArray):Boolean {
return false; }
It should give the following error:
Error: Implicit coercion of a value of type (input:ByteArray)=>Boolean to
an unrelated type (input:String)=>Boolean.
The syntax supports optional parameters and rest parameters. Optional
parameters would be equivalent to parameters that have a default value in a
regular function signature. However, you don't need to specify the default
value in the function type expression (assigned functions are allowed to
have different default values or to use rest instead), and you may use the
? token to indicate that a specific parameter is optional.
var func:(s?:String, ...rest):void;
You can even nest function type expressions.
var action:(callback:(result:Object)=>void):void;
I've created some documentation to help folks get started:
https://apache.github.io/royale-docs/features/as3/strict-function-types
--
Josh Tynjala
Bowler Hat LLC
https://bowlerhat.dev/
