Allow rest parameter may not be the last one.

[heroboy]

For example, a function takes any number of parameters and return the last one.

function GetLastOne<T>(...rest:any[], last:T)
{
    return last;
}

and this: http://createjs.com/docs/easeljs/classes/Container.html#method_addChild

[kitsonk]

That is not valid ES6, therefore I suspect the TypeScript team will not be interested in implementing it. Even then it is tricky... The clue is in the name (rest) as in: "the rest of the arguments". How would you propose to deal with:

GetLastOne(undefined, undefined);
/* or */
GetLastOne(1, 2, undefined);
/* or depending on what you would suggest to emit this */
GetLastOne(undefined, 1, undefined, 2);

[heroboy]

I want this because I want a strong typed way to declare a function like http://createjs.com/docs/easeljs/classes/Container.html#method_addChild .

GetLastOne(undefined, undefined);
/* or */
GetLastOne(1, 2, undefined);
/* or depending on what you would suggest to emit this */
GetLastOne(undefined, 1, undefined, 2);

And what's the problem with the codes?
for the 1st and 2nd the type T is undefined,and last is undefined.
I think GetLastOne can emit like this:

//function GetLastOne<T,U>(first:U,...rest:any[], last:T)
function GetLastOne()
{
    var first = arguments[0];
    var rest = [];
    for(var i=1;i<arguments.length-1;++i)
        rest.push(arguments[i]);
    var last = arguments[arguments.length-1];
}

[danquirk]

@heroboy Beyond the issues mentioned I'm not sure I understand why you need this feature for addChild. The signature should just be:

interface Container {
    addChild(child: DisplayObject): DisplayObject;
    addChild(...children: DisplayObject[]): DisplayObject;
}

That the implementation of the second overload returns children[children.length-1] (as opposed to any other element of children) is not something that is encoded in the type system.

[danquirk]

In any case, this is a duplicate of #1360

[heroboy]

@danquirk Because I want

container.addChild(new Text()).text = "xxxx";

not

(<Text>container.addChild(new Text())).text = "xxxx";

[danquirk]

Then you just need a generic declaration of addChild:

interface DisplayObject {
        name: string;
    }

    class Text implements DisplayObject {
        name: string;
        text: string;
    }

    interface Container {
        addChild<T extends DisplayObject>(child: T): T;
        addChild<T extends DisplayObject>(...children: T[]): T;
    }

    var c: Container;
    var r = c.addChild(new Text()).text;
    var r2 = c.addChild(new Text(), new Text()).name;

[heroboy]

class Shape implements DisplayObject {
    name:string;
}
//then this is not allowed.
c.addChild(new Shape(), new Text()).text = "xxx";