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I have the following code:

bool do_something_conditional(int *handle, const boost::function<bool(int)> &pred); bool pred_a(int handle); bool pred_b(int handle, int n1, int n2);

bool do_something(int *handle, int n1, int n2) { return do_something_conditional(handle, boost::bind(std::logical_and<bool>(), boost::not1(&pred_a), boost::bind(&pred_b, _1, n1, n2))); }

But it does not compile.

This should work and is probably clearer:

return do_something_conditional(handle, boost::bind(std::logical_and<bool>(), !boost::bind(&pred_a, _1), boost::bind(&pred_b, _1, n1, n2)));

Yes, it works. Thank you, Ben. But why is my way wrong? With either boost::not1(&pred_a) or !boost::bind(&is_master_device, _1) we get a functor that takes 1 parameter of type int. Max

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I have the following code:

bool do_something_conditional(int *handle, const boost::function<bool(int)> &pred); bool pred_a(int handle); bool pred_b(int handle, int n1, int n2);

bool do_something(int *handle, int n1, int n2) { return do_something_conditional(handle, boost::bind(std::logical_and<bool>(), boost::not1(&pred_a), boost::bind(&pred_b, _1, n1, n2))); }

But it does not compile.

This should work and is probably clearer:

return do_something_conditional(handle, boost::bind(std::logical_and<bool>(), !boost::bind(&pred_a, _1), boost::bind(&pred_b, _1, n1, n2)));

Yes, it works.

Thank you, Ben.

But why is my way wrong? With either boost::not1(&pred_a) or !boost::bind(&is_master_device, _1) we get a functor that takes 1 parameter of type int.

I don't know. I think there is some kind of voodoo in boost::bind that means the outer bind will evaluate the inner bind, bot won't try to evaluate not1.

The "voodoo" is described here: http://www.boost.org/doc/libs/1_49_0/libs/bind/bind.html#nested_binds Basically, bind treats nested binds specially, precisely to allow the sort of thing the OP's trying to do. Regards, Nate

Ben Pope wrote:

Or even

return do_something_conditional(handle, !boost::bind(&pred_a, _1) && boost::bind(&pred_b, _1, n1, n2) );

As for the original error,

error C2664: 'bool std::logical_and<_Ty>::operator ()(const _Ty &,const _Ty &) const' : cannot convert parameter 1 from 'boost::unary_negate<Predicate>' to 'const bool &'

the compiler is right, logical_and doesn't accept boost::not1(&pred_a) as a first argument, it takes a bool. To make it compile, one needs to wrap boost::not1(&pred_a) in a boost::bind, as follows:

bool do_something(int *handle, int n1, int n2) { return do_something_conditional(handle, boost::bind(std::logical_and<bool>(), boost::bind(boost::not1(&pred_a), _1), boost::bind(&pred_b, _1, n1, n2))); }

This will call boost::not1(&pred_a) with _1 instead of passing it as-is to logical_and.

Thank you for your swiss army knife, Peter. Max