Regarding Issue 9423

[Maxim Fomin]

On Wednesday, 30 January 2013 at 11:10:17 UTC, bearophile wrote:
> Currently you are allowed to write a lambda literal as in line 
> 3, but you can't omit "ref" as in line 4:
>
>
> void foo(int delegate(ref int[1]) spam) {}
> void main() {
>     foo((ref x) => 0); // line3, OK
>     foo(x => 0); // line4, Error
> }
>
>
> Do you think "ref" annotation should be required at the call 
> site?

Ref isn't at a call site, it is a function declaration and not 
passing lambda by ref.

> This is the Bugzilla thread. Hara has already implemented the 
> "ref" inference, but he's not sure if it's a good idea:
>
> http://d.puremagic.com/issues/show_bug.cgi?id=9423
>
> Bye,
> bearophile

int delegate(ref int[1] spam) and
int delegate(int[1] spam) are different.

True, the proposal makes code writing convenient, but it can lead 
to troubles when foo has overload with non-ref parameter 
delegate. This also may probably lead to problems when passed by 
delegate function modifies its argument but it is unexpected by 
user because function was not annotated with ref. Moreover, this 
is a special case in a language.