[boost] Re: Bizarre Lambda bind() problem with Base class types

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2005-01-07 17:32:16

Brian Braatz wrote:
> With the following code, If you UNCOMMENT the "// public : Base" line,
> you get compiler errors (????)
> 
> I have tested this with MS VC 7.1 against both 1.31 and 1.32 versions of
> boost with the same results.
> 
> Any idea why this is happening? (full sample code I wrote is attached)
>[snip]
> 			std::string ReturnAString();
 > [snip]
> 				bind(Base::ReturnAString,_1);

This is the problem. Try:
    bind(Base::ReturnAString);
or:
    bind(&Base::ReturnAString,this);

> My Compiler errors are this:
> 
> c:\Data\Rmtg\Root\_Common\_Lib\Rmx\V_0_02\Exp\Src\LambdaProblem\Test_Lam
> bdaProblem.cpp(38) : error C2780: 'const
> boost::lambda::lambda_functor<... >
> boost::lambda::bind(...)' : expects 10 arguments - 2 provided

The error is misleading. I got a similar error when using Boost.Bind in 
my GUI code. The basics of it is this: the arguments of bind(fn, ...) 
must match to the arguments of the function *exactly*, using _n for 
unspecified arguments. What this means is:

using boost::bind;
using boost::function;

class button
{
    void draw( event * ev );
};

button btn;

function< ( event * ) > foo = bind(&button::draw,&btn); // [1]
foo = bind(&button::draw,&btn,_1); // _1 needed for the event * argument

[1] generates a similar error message to the one you get above.

Maybe this should be mentioned in the documentation somewhere.

HTH,
Reece