Why don't lazy parameters bind to delegates? Was: Feature to get or add value to an associative array.

[Jonathan M Davis]

On Friday, April 20, 2018 19:27:20 Steven Schveighoffer via Digitalmars-d 
wrote:
> On 4/20/18 6:46 PM, Giles Bathgate wrote:
> > On Friday, 20 April 2018 at 22:21:13 UTC, Jonathan M Davis wrote:
> >> Honestly, I think that it's a terrible idea to special-case it like
> >> that. If we want to argue for making it work in the language, that's
> >> fine, but if we special-case it like this, then it will work with some
> >> functions that have lazy parameters and not others, and the result
> >> will be confusing. Besides, all it takes to be able to pass a lamdba
> >> or delegate to a lazy parameter is to actually call it when passing
> >> it. So, if you add parens after the braces, it works. There's no need
> >> to go and add a special case for it to the function.
> >
> > Again lack of experience, so I presume you can just do:
> >
> > bool inserted = false;
> > auto p = aa.getOrAdd("key", {inserted = true; return new Person; }());
> >
> > I hadn't realised that until now. I enjoy your brutal honesty by the way
> > ;)
> The drawback here, of course, is that it's a lambda calling a lambda (if
> you end up using the value).
>
> But of course, your overload was the same thing.
>
> I'm just surprised it doesn't work, especially when this works:
>
> // lazy variadic
> void foo(int delegate()[] dgs...)
> {
>     dgs[0]();
> }
>
> foo(1); // ok, same as { return 1; }
> foo({inserted = true; return 1;}); // ok
>
> Of course, it's not as nice syntax inside the function.

Honestly, I would have considered it a bug that it accepts 1, since that's
not a delegate or lambda or anything of the sort, and the function is
explicitly typed to take delegates.

- Jonathan M Davis