lazy redux

[Leandro Lucarella]

Michal Minich, el  7 de diciembre a las 13:51 me escribiste:
> Hello Denis,
> 
> >>1. auto t = new Thread ( { a=42 } );
> >>or auto t = new Thread ( () { a=42 } );
> >It already works, just try it (but don't forget to put a semicolon at
> >the  end).
> >
> >>2. array.findAll (arr, (item) { item.contains ("abc") } ); 3. foo (
> >>(a, b) { a + b } );
> >>
> >>4. array.findAll (arr, (item) { return item.contains ("abc"); } );
> >>
> >>I'm not proposing this syntax (maybe I probably should, but I have
> >>feeling I would not be first). It may not even be possible to parse
> >>it,  but seems to me more similar to how currently functions are
> >>written. In  this setting {exp} or {stm} is not *special* case.
> >>
> >I believe it would work. And yes, it was already proposed by many
> >others.
> >
> 
> it works with two differences:
> 
> 1. the semicolon is required, even if the body consist only of one
> expression. This is a minor detail.
> 2. more importantly - parameter types must be specified explicitly.
> I don't understand why type of b cannot be inferred in this example:
> 
> void foo (void delegate (int a) dg)
> {
>    dg(1);
> }
> 
> void main ()
> {
>    foo ( (int b)  { writeln (b); } );
> }

It doesn't do implicit returning either:

$ cat -n x.d
     1	
     2	import std.stdio;
     3	
     4	void foo (int delegate() dg)
     5	{
     6		writeln(dg());
     7	}
     8	
     9	void main()
    10	{
    11		int a = 5;
    12		foo({a;});
    13	}
    14	
$ dmd x.d
x.d(12): Error: var has no effect in expression (a)
x.d(12): Error: function x.foo (int delegate() dg) is not callable using argument types (void delegate())
x.d(12): Error: cannot implicitly convert expression (__dgliteral1) of type void delegate() to int delegate()

To make it work you have to do it like this:
    12		foo({return a;});

Which is considerably uglier than
    12		foo({a});

At least when talking about replacing "lazy" :)

Nobody wants to write:
enforce({ return a == 5; });
instead of:
enforce(a == 5);

But:
enforce({a == 5});

Could be acceptable.


-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
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