[Issue 9149] Disallow converting delegates to const

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=9149

--- Comment #12 from Steven Schveighoffer <schveiguy at yahoo.com> ---
Yes I see.

The issue is the conversion of the delegate type, when the context pointer is
changed to const (but you didn't change the function pointer, so it still
assumes it's argument is mutable).

I agree with you.

So basically, any struct or class instance cannot convert to const (or via pure
constructor to immutable) if it contains a non-const delegate. Yuck, but I
think we have to do that.

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