static `this`

[Meta via Digitalmars-d]

On Sunday, 8 February 2015 at 00:31:42 UTC, Mike wrote:
> I'm elevating this from D.Learn [1] because I think it needs 
> some input from the language designers.
>
> This code compiles and executes:
> -----------------------------------
> import std.stdio;
>
> struct StaticRegister {
>     static private uint _value;
>     @property static uint value() { return _value; }
>     @property static void value(uint v) { _value = v; }
>
>     static alias value this;
>
>     static void test() {
>         writeln(this.stringof);
>         writeln(typeof(this).stringof);
>         writeln(this.value);
>     }
> }
>
> void main(string[] s) {
>     // works due to `alias value this`
>     StaticRegister = 1;
>
>     StaticRegister.test();
> }
> -----------------------------------
>
> Output:
> StaticRegister
> StaticRegister
> 1

`this` should not exist within a static member function. The fact 
that this code compiles is probably a bug. `StaticRegister = 1` 
is almost definitely not intended behaviour, and I don't know 
about `static alias value this`.


> However, this code fails to compile:
> -----------------------------------
> struct StaticRegister {
>     static void test() {
>         assert(this is null);
>     }
> }
>
> void main(string[] s) {
>     StaticRegister.test();
> }
> -----------------------------------
>
> Output:
> test.d(5): Error: 'this' is only defined in non-static member 
> functions, not test

This is correct behaviour.


> Is `this` overloaded to mean "this class" in a static context 
> or is `this` only valid in a non-static context.  Please 
> clarify, and if it's a bug, help me understand so I can make an 
> accurate and actionable bug report.

`this` should only be valid in a non-static context, as far as I 
know. That's pretty much what static means: "there is no `this`".