Anonymous function syntax

[Christophe]

Andrei Alexandrescu , dans le message (digitalmars.D:145023), a écrit :
>> What is the problem with just inferring the `return`, allowing you to replace
>>       (a,b) { return a + b; }
>>
>> with
>>      (a, b) { a + b; }

> The objection is that it introduces a number of questions:
> 
> 1. How about using that syntax in regular functions?
> 2. What if the lambda wants to actually evaluate the expression but 
> return void?
> 3. How is the semicolon relevant? (If its presence is used as a 
> disambiguator for (2), it's poor design to predicate a large semantic 
> difference on such a distinction.)

I think such shortcut should be allowed only for one-liners. There is no 
gain not to write return if you already have several statements.
The shortcut syntax should be
  (a, b) { expression },
and not
  (a, b) { statement } 

This way, you ensure that only one liners can use this syntax, so there 
is no abuse.

It is true that the return type would depend on the presence of a 
semicolon, but the compiler will quickly complain if it expects a 
delegate returning void and gets a delegate returning a type, or 
vice-versa anyway.

>> Also would it make sense to have a template library along the lines of boost::proto/boost::lambda to allow even
>> shorter, expression-based lambdas like
>>
>>      _1 + _2
>>
>> I'm not exactly a D template metaprogramming pro, but I think this would work for a lot of common cases.
> 
> Such an approach has caused more trouble than benefits in C++.

Too dangerous. std.algorithm uses a, b, c, etc, but it can only do that 
because it never checks the context:

int b;
double x;
auto f = lambda { a * x + b }

How many arguments does f take ?

-- 
Christophe