Re: [boost] determine first arg of callable

Subject: Re: [boost] determine first arg of callable
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2013-05-15 09:13:12

2013/5/15 Mathias Gaunard <mathias.gaunard_at_[hidden]>

> On 15/05/13 10:35, Oliver Kowalke wrote:
>
>> I need some help to extract the type of a callable which is passed as
>> argument to the ctor of X.
>>
>> struct X
>> {
>>    template< typename Fn >
>>    X( Fn fn) {
>>         ... code which evaluates Fn and extracts the type of the first arg
>> of Fn
>>     }
>> };
>>
>
> You can't do that.
> Just change your code to not require it.
>

that is not possible

at least what I can do is to overload the ctor:

template< typename Arg >
X( void(*fn)( Arg &) ) {...}

template< typename Arg >
X( boost::function< void( Arg &) > fn) {...}

ctor is called then:

X x1( g); // OK

A a;
boost::function< void( Y< char > &) > f1=boost::bind( & A::operator(), a,
_1);
X x2( f1);

boost::function< void( Y< int > &) > f2=boost::bind( g, _1);
X x3( f2);

For function pointer it's OK - but the code using function<> and bind()
looks a little bit clumsy:

X x2(boost::bind( & A::operator(), a, _1)); // will not compile