Re: [Boost-users] lambda - if_then_else - Compiler can not deduce my Arguments

Subject: Re: [Boost-users] lambda - if_then_else - Compiler can not deduce my Arguments
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2011-03-28 05:16:26

On Monday, March 28, 2011 11:34:45 AM Simon Adler wrote:
> Hello,
> 
> i need a hint about boost::bind and lambda.
> Following (reduced) case:
> 
> class XML_Element
> {
>   public:
>      const std::string & getName(void);
> };
> 
> class HandleStuff
> {
> void handleTransformations( XML_Element * node );
> void handleLinks( XML_Element * node );
> 
> 
> void handle ( std::list<XML_Element *> * nodes )
> {
> // what i want to do via boost and which will do the job
> for (std::list< XML_Element *>::iterator it = nodes->begin(); it !=
> nodes->end(); it++)
> {
>   if ( (*it)->getName() == "Transform" ) handleTransformations(*it);
>   else handleLinks(*it);
> }
> 
> // what i tried
> std::for_each( nodes->begin(); nodes->end(),
>    boost::lambda::if_then_else( boost::bind(&XML_Element::getName, _1) ==
> std::string("Transform"),
> 
>  boost::bind<void>(&HandleStuff::loadTransformations, this, _1),
> 
>  boost::bind<void>(&HandleStuff::loadLinks, this, _1) )
> }
> 
> }

The error you made is that you mixed boost bind with lambda, which is not 
compatible.

A solution with Phoenix looks like this:

        using boost::phoenix::arg_names::_1;
        using boost::phoenix::bind;
        using boost::phoenix::if_;
        
        std::for_each( nodes->begin(), nodes->end(),
            if_(bind(&XML_Element::getName, _1) == "Transform")
            [
                bind(&HandleStuff::handleTransformations, this, _1)
            ]
            .else_
            [
                bind(&HandleStuff::handleLinks, this, _1)
            ]
        );

> got an error, that the compiler can not deduce a template Argument, but i do
> not understand what
> the compiler tries to say.
> 
> I am new to bind and lambda and i like it a lot, but in some cases the
> Error-Messages are hard to
> understand.
> 
> Thank you for any advice. Please understand, that this example is a reduced
> Version what is realy
> going on, so i only give the Functions Interfaces.
> 
> Simon
>