Re: [Boost-users] [boost lambda bind] overloading not compiling

Subject: Re: [Boost-users] [boost lambda bind] overloading not compiling
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2012-04-13 01:41:13

On 04/13/2012 03:07 AM, Jeffrey Lee Hellrung, Jr. wrote:
> On Thu, Apr 12, 2012 at 3:02 PM, Kaz<sfx810_at_[hidden]>  wrote:
>
>> Hi All, I came across this strange error. Binding of overloaded member
>> functions works with boost bind, but not with boost lambda bind. Here
>> is the example
>>
>> Following builds and works fine
>>
>> #include "boost/function.hpp"
>> #include "boost/bind.hpp"
>>
>> class Operations
>> {
>> public:
>>         void Fun1( int i ){ std::cout<<"\nfunction with one arg\n";     }
>>         void Fun1( int i, double d)     {std::cout<<"\nfunction with two
>> args\n"; }
>> };
>> -----------------------
>> int main()
>> {
>>         Operations op;
>>         typedef boost::function<void ()>   fptr;
>>         fptr func1 = boost::bind(&Operations::Fun1,&op,1);
>>         fptr func2 = boost::bind(&Operations::Fun1,&op, 1, 2.2 );
>>               return 0;
>> }
>>
> I'm kind of surprised this works. Perhaps bind infers the correct arity
> given the number of parameters, and based on the arity, the compiler is
> able to deduce which overload of Fun1 you want. In any case, it probably
> wouldn't work if you overloaded Fun1 on argument type only.
Correct. Boost.Bind is deducing the correct function pointer. Your 
assumption is correct that when overloading only on one argument, it fails.
I was as surprised as you are, however, this works for phoenix too. If 
the OP really needs more functionality than provided by bind, he should 
go with phoenix.
>
>
>> ------------------------
>> While following Does not compile
>>
>> int main()
>> {
>>         using namespace boost::lambda;
>>         Operations op;
>>         typedef boost::function<void ()>   fptr;
>>         fptr func1 = bind(&Operations::Fun1,&op,1);
>>         fptr func2 = bind(&Operations::Fun1,&op, 1, 2.2 );
>>               return 0
>> }
>>
>> -------------------------
>>
>> This spits out massive error, as shown below. I think gist of which is
>> it can't figure out which function to instantiate, when using lambda
>> bind. Can some body please point out what am I missing here ?
>>
> I'm guessing that, unlike boost::bind, boost::lambda::bind is not
> overloaded directly for member function pointers. In any case, you're
> probably asking for trouble with expressions like&Operations::Fun1 when
> Fun1 is overloaded :/
>
>
>> (Sorry for long email, I didn't wanted to clutter the email with this
>> error message, bu thought most of you will figure it out just from
>> looking at it.).
>> Any help will be appreciated, and thanks in advance.
>> Kaz
>>
>> boostFunctionAndBind.cpp: In function ‘int main()’:
>> boostFunctionAndBind.cpp:61:45: error: no matching function for call
>> to ‘bind(<unresolved overloaded function type>, Operations*, int)’
>> boostFunctionAndBind.cpp:61:45: note: candidates are:
>>
> [...snip candidates...]
>
> - Jeff
>
>
>
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