DIP30, delegates more destruction for your pleasure

[kenji hara]

2013/3/14 deadalnix <deadalnix at gmail.com>
>
> It is a tempting idea, but do not work. Consider :
>
> void delegate() immutable a;
> const void delegate() b = a;
>
> This would be forbidden as covariance of function parameters and
> transitivity act in opposite directions.
>

You are misunderstanding about delegate type syntax and transitivity.

1. This qualifier for delegate type should be added after parameter types.

const void delegate() b;   // bad, typeof(b) == const(void deelgate())
void delegate() const b;   // good, b can hold const method

2. A delegate which has immutable context cannot implicitly convertible to
const context delegate.

In general, if a delegate can implicitly convertible to another, there
should be _contravariance_ of parameter types.

void delegate() immutable a;
void delegate() const b;
b = a;  // bad
a = b;  // good

Kenji Hara
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