Forwarding or merging 'this' into a child class to aid chaining methods?

[anonymous]

On Thursday, 6 March 2014 at 19:04:50 UTC, Gary Willoughby wrote:
> I'm trying to create methods across class hierarchies that can 
> be chained nicely but i'm running into the problem that 'this' 
> declared in a parent class only refers to that type. Is there a 
> way i can get the following code to perform in the way i expect?
>
> import std.stdio;
>
> class Foo
> {
> 	public auto foo()
> 	{
> 		return this;
> 	}
> }
>
> class Bar : Foo
> {
> 	public auto bar()
> 	{
> 		return this;
> 	}
> }
>
> void main(string[] args)
> {
> 	Bar bar = new Bar().bar().foo();
> }
>
> test2.d(21): Error: cannot implicitly convert expression ((new 
> Bar).bar().foo()) of type test2.Foo to test2.Bar
> Failed: 'dmd' '-v' '-o-' 'test2.d' '-I.'
>
> How can i make the above marked 'this' refer to Bar when being 
> called in a chain? When i call the methods like this each 
> method call seems to implicitly convert 'this' into that 
> method's containing class' instance, breaking the code and 
> sometimes hiding child methods.

	public auto foo(this T)()
	{
		return cast(T) this;
	}

http://dlang.org/template.html#TemplateThisParameter