On Thu, Jan 09, 2014 at 09:49:17AM +0100, Jacob Carlborg wrote:
> On 2014-01-08 19:04, H. S. Teoh wrote:
[...]
> >In fact, we can already almost get the desired syntax in the current
> >language:
> >
> > /* Current D already supports this: */
> > range.my_foreach!((i,j) {
> > /* body */
> > });
>
> Almost ;)
>
> >which isn't that much different from the proposed syntactic sugar:
> >
> > range.my_foreach(i,j) {
> > /* body */
> > }
> >
> >We're just saving on the '!', ';', and an extra pair of parentheses.
>
> It quickly get clumsy when you need to pass regular arguments to the
> function:
>
> void foo (alias dg) (int a, int b);
>
> foo!((i, j) {
> // body
> })(1, 2);
>
> Not pretty.
True. So this should be one of the motivating use cases for our DIP.
> >I guess the only real advantage is that we get to imitate built-in
> >foreach syntax. E.g., if we use the form with arguments but no
> >indexing arguments, we can pretend to be an if-statement:
> >
> > // (Whatever "dynamic if" means...)
> > void dynamic_if(alias dg)(bool cond)
> > if (is(typeof(dg())))
> > {
> > // Haha, we're just wrapping the built-in 'if' cuz we
> > // can.
> > if (cond) dg();
> > }
> >
> > int x;
> > dynamic_if (x==0) {
> > writeln("Boo yah!");
> > }
> >
> >Or if we use the argumentless form to implement custom block constructs:
>
> BTW, what do you think about not needing braces if the delegate body
> only contains a single statement, like with regular statements:
>
> dynamic_if (x==0)
> writeln("foo");
>
> With the alias syntax, I'm wondering if the compiler will have any
> problem with that you can pass almost anything to an alias parameter
> and not just a delegate.
[...]
I'm afraid that this might become ambiguous, for example:
int* gun(...) {...}
func (x==0)
*gun(y);
Does the second statement mean `func!(() => *gun(y))(x==0)`, or does it
mean `func(x==0) * gun(y)`? While it's not hard to disambiguate this
semantically, it means it's impossible to parse before you analyze it,
which is probably a bad idea.
T
--
Nobody is perfect. I am Nobody. -- pepoluan, GKC forum
