Re: [Boost-users] Boost.Function compile error

Subject: Re: [Boost-users] Boost.Function compile error
From: gast128 (gast128_at_[hidden])
Date: 2013-03-07 08:15:27

On 3/7/2013 1:00 PM, Igor R wrote:
>>> It's because the compiler threats
>>> Bla(id);
>>> as:
>>> Bla id;
>>> as you can see from the errors (MSVC10):
>>> error C2371: 'id' : redefinition; different basic types
>>> error C2512: 'Bla' : no appropriate default constructor available
>>
>>
>> Yes but which (obscure) c++ rule allows this. My day to day c++ knowledge
>> says that () is only used for macro invocations, function declarations,
>> function call's and cast operators and none of them seems to be applicable
>> here.
>
>
> I belive this falls under the paragraph 6.8:
> "There is an ambiguity in the grammar involving expression-statements
> and declarations: An expression-statement with
> a function-style explicit type conversion (5.2.3) as its leftmost
> subexpression can be indistinguishable from a declaration
> where the first declarator starts with a (. In those cases the
> statement is a declaration."
>
> While paragraph 5.1 (5) says:
> "A parenthesized expression is a primary expression whose type and
> value are identical to those of the enclosed expression.
> The presence of parentheses does not affect whether the expression is
> an lvalue. The parenthesized expression can
> be used in exactly the same contexts as those where the enclosed
> expression can be used, and with the same meaning,
> except as otherwise indicated."
>
> Try the following :)
>
> int (main())
> {
> }
>
a thx. The standard wording is too cryptic for me but there is an 
explanation. I should switch to c# :).