Re: [Boost-users] [Bind] How to create a functor which returns one ofits arguments?

Subject: Re: [Boost-users] [Bind] How to create a functor which returns one ofits arguments?
From: Peter Dimov (pdimov_at_[hidden])
Date: 2009-12-08 19:10:19

Vadim Guchenko wrote:
> Hello, All!
>
> Is there a simple way to create a functor that returns one of its
> arguments _1, _2, ...?
> Does standard unary functor exist, which simply returns its argument
> unchanged? I.e.:
>
> template<typename T>
> struct arg: public std::unary_function<T, T> {
>        T operator()(const T &x) const { return x; }
> };

It's not part of the current standard, but many implementations provide 
std::identity as an extension. (It will be standard in C++0x.)