Re: [boost] Report from Berlin C++ Standards Committee meeting

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-04-13 11:05:19

Jaakko Jarvi wrote:
> On Apr 12, 2006, at 4:18 PM, Peter Dimov wrote:
> 
>> I'd prefer to not be forced to spell the type of the arguments:
>> 
>>     inline bool less( x, y ) { return x < y; }
>> 
>> (and live with the ambiguities when x is a type in an outer scope)
>> but even
>> with explicit typing as in N1958 it's much better than nothing. :-)
> 
> The syntactic trouble (which I believe Peter is referring to with the
> comment on ambiguities)
> is that in a normal function parameter list one can leave out the
> parameter name, here we would
> be leaving out the parameter type. I think that is fine, but I'd thus
> rather make lambdas
> look different so that there is no confusion of what kind of
> parameter list we are dealing with.
> 
>   (e.g. with the syntax <>(x, y) { return x < y; } )
> 
> Flagging an ambiguity in the case that the parameter name would be a
> type in an outer scope seems quite brittle.

But I should also note that there are three cases:

1. Lambdas require explicit argument types, as ordinary functions do;
2. Lambdas do not have explicit argument types (as in the above examples);
3. Lambdas allow explicit argument types but do not require them.

The ambiguity arises only in (3). (1) and (2) don't have this problem.