Problem with boost::bind and boost::lambda::bind
I'm a newbie to the boost library so I need some help with the
following problem:
Take the following code:
class EaSde // Abstract class.
{
...
public:
inline virtual double unitDiffusionInverseMap( double x ) const = 0;
inline virtual void unitDiffusionInverseMap( Path& path ) const;
....
};
void EaSde::unitDiffusionInverseMap( Path& path ) const
{
std::transform( path.values.begin(), path.values.end(), path.values.begin(),
boost::bind<double>( &sde::EaSde::unitDiffusionInverseMap, this, _1 ) );
}
This code works fine.
However if I use boost::bind::lambda instead of boost::bind I get:
1>Compiling...
1>sdefunctionalmc.cpp
1>c:\develop\nsde\nsde\abstracteasde.hpp(58) : error C2664: 'const
boost::lambda::lambda_functor<T> boost::lambda::bind
Stefano Peluchetti
I'm actually moving everything to boost::lambda::bind to 1) avoid the conflict of boost::lambda::_1 and _1 2) have binders that are "lambda ready" if needed
Thank you in advance for your reply.
Note that sometimes boost::bind is a better choice that boost::lambda::bind. 1. boost::bind has better support for smart pointers. struct A { void f() {} }; shared_ptr<A> a; bind(&A::f, _1)(a); // works for boost::bind only 2. boost::bind sometimes can choose correct instance of overloaded function. (probably you got hit by this distinction). struct A { void f() const {} void f() {} }; A a; bind(&A::f, a); // works for boost::bind only 3. boost::bind can accept non-const rvalue if there are not many arguments. I believe last (unreleased) version of boost::lambda::bind can do this as well. void f(int) {} bind(f, _1)(42); // works for boost::bind only My personal experience also shows that boost::bind based code compiles faster. Roman Perepelitsa.
Roman Perepelitsa
Stefano Peluchetti
writes: I'm actually moving everything to boost::lambda::bind to 1) avoid the conflict of boost::lambda::_1 and _1 2) have binders that are "lambda ready" if needed
Thank you in advance for your reply.
Note that sometimes boost::bind is a better choice that boost::lambda::bind.
1. boost::bind has better support for smart pointers.
struct A { void f() {} };
shared_ptr<A> a; bind(&A::f, _1)(a); // works for boost::bind only
2. boost::bind sometimes can choose correct instance of overloaded function. (probably you got hit by this distinction).
struct A { void f() const {} void f() {} };
A a; bind(&A::f, a); // works for boost::bind only
3. boost::bind can accept non-const rvalue if there are not many arguments. I believe last (unreleased) version of boost::lambda::bind can do this as well.
void f(int) {}
bind(f, _1)(42); // works for boost::bind only
My personal experience also shows that boost::bind based code compiles faster.
Roman Perepelitsa.
Very interesting information, thank you. Is there any documentation about these details ? I couldn't find anything like that in the boost lambda library documentation. I noticed that boost::bind code usually compiles faster too. But I'm working an a numerical simulation library and I have to compose functions together a lot of times. That's where lambda is very handy. Also I can't still understand *why* only the boost::bind binder works in the three examples you gave. What is the technical reason behind these results? Is it really necessary to study the whole boost::lambda library from source code to figure it out? Best Regards
Stefano Peluchetti
Very interesting information, thank you. Is there any documentation about these details ? I couldn't find anything like that in the boost lambda library documentation.
I noticed that boost::bind code usually compiles faster too. But I'm working an a numerical simulation library and I have to compose functions together a lot of times. That's where lambda is very handy.
Also I can't still understand *why* only the boost::bind binder works in the three examples you gave. What is the technical reason behind these results? Is it really necessary to study the whole boost::lambda library from source code to figure it out?
Best Regards
AFAIK, there are no reasons for not supporting this stuff in lambda bind, except one -- it requires time for implementation. Some day we'll have both of two worlds -- phoenix 2. It should unite boost bind, boost lambda and phoenix. I believe no one is seriously interested in improving boost lambda at the moment because this code gonna become obsolete soon. Roman Perepelitsa.
Stefano Peluchetti wrote:
I'm a newbie to the boost library so I need some help with the following problem: Take the following code:
class EaSde // Abstract class. { ... public: inline virtual double unitDiffusionInverseMap( double x ) const = 0; inline virtual void unitDiffusionInverseMap( Path& path ) const; .... };
void EaSde::unitDiffusionInverseMap( Path& path ) const { std::transform( path.values.begin(), path.values.end(), path.values.begin(), boost::bind<double>( &sde::EaSde::unitDiffusionInverseMap, this, _1 ) ); }
This code works fine. However if I use boost::bind::lambda instead of boost::bind I get:
... Bind libraries in general have trouble with overloaded functions; this is a limitation of C++. boost::bind is slightly better than lambda::bind in such cases. No, there is no list of the differences between boost::bind and lambda::bind. FWIW, I wasn't aware of the above difference in behavior, so the list wouldn't have had it anyway. :-)
participants (3)
-
Peter Dimov -
Roman Perepelitsa -
Stefano Peluchetti