using boost::lambda or boost::phoenix with std::find_if

Question

I have a class like this

class Foo {
    public:
        int GetID() const { return m_id; }
    private:
        int m_id;
};

I want to use find_if on a vector full of Foo objects, like this:

std::find_if(foos.begin(), foos.end(), ???.GetID() == 42);

I don't quite get what I have to write instead of ???. I know there is either _1 with boost::lambda or arg1 with boost::phoenix, but after that I'm at a loss.

Edit:

I tried the following which does not work, even though I saw it like this in many examples.

std::find_if(foos.begin(), foos.end(), boost::lambda::bind(&Foo::GetID, boost::lambda::_1) == 42);

Then I get the following error:

error C2678: binary '==' : no operator found which takes a left-hand operand of type 'const boost::lambda::lambda_functor' (or there is no acceptable conversion)

why doing it to yourself when you can use the c++11 standard? — David Haim, Sep 03 '15 at 12:40
`std::find_if(foos.begin(), foos.end(), (&boost::phoenix::placeholders::_1->*&Foo::GetID)() == 42);` — Piotr Skotnicki, Sep 03 '15 at 12:47
@Piotr Skotnicki: That gives me the error: cannot convert from 'const boost::phoenix::actor *' to 'const Foo *' — gartenriese, Sep 03 '15 at 12:50

ForEveR · Accepted Answer · 2015-09-03T12:59:58.563

4

Use boost::bind for this case, it's really the easiest way before C++11.

std::find_if(foos.begin(), foos.end(), boost::bind(&Foo::GetId, _1) == 42);

If you should use phoenix you can use phoenix::bind.

std::find_if(foos.begin(), foos.end(),
phx::bind(&Foo::GetId, phx::placeholders::_1) == 42);

where phx is

namespace phx = boost::phoenix;

If you can use C++11 - you can use std::bind, or lambda function

std::find_if(foos.begin(), foos.end(), 
[](const Foo& f) { return f.GetId() == 42; });

edited Sep 03 '15 at 12:59

answered Sep 03 '15 at 12:41

ForEveR

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@gartenriese you are trying wrong. In my example is just boost bind, not boost lambda bind. And look at my example, in your example there is no compare with actual value. – ForEveR Sep 03 '15 at 12:49
Oh my. If I use boost::bind instead of boost::lambda::bind, it works. Thanks a lot, I'd never guessed! – gartenriese Sep 03 '15 at 12:53
The `phoenix` version does not work like you explained though. – gartenriese Sep 03 '15 at 12:59
@gartenriese work as well. Look: http://coliru.stacked-crooked.com/a/0e027c53f781ff63 – ForEveR Sep 03 '15 at 13:00
Huh, now it works. I must've forgotten some headers. Thanks! – gartenriese Sep 03 '15 at 13:10
I'm not sure `boost::bind(...)==42` would work. Does it overload `==` ? – Nawaz Sep 03 '15 at 14:19
@Nawaz yep. `boost::bind` has all compare operators overloaded. http://www.boost.org/doc/libs/1_55_0/libs/bind/bind.html#operators – ForEveR Sep 03 '15 at 14:37

using boost::lambda or boost::phoenix with std::find_if

1 Answers1