change 'this' pointer for structs to reference type

[Frits van Bommel]

Walter Bright wrote:
> Frits van Bommel wrote:
>> I think "typeof(this) == S*" is the current situation. What they're 
>> suggesting is "typeof(this) == ref S".
> 
> Not exactly, ref is not a type constructor. typeof(this)==S

As long as it's still a reference, that's close enough for 'this' :).