On Tue, Nov 30, 2010 at 3:20 PM, Steven Watanabe wrote:

AMDG

On 11/30/2010 7:06 AM, Robert Jones wrote:

...

I'm not sure if this is a stupid question, but is there a runtime equivalent of boost.mpl's identity metafunction?

Something that just returns it's single argument, eg.,

template<typename T> T identity( T t ) { return t; }

I think it's trivially simple to write, but I wonder if it already exists in Boost or indeed the STL?

(I need this because I need to pass a function object which simply returns an object I already have - maybe I've missed a more obvious method?)

boost::lambda::_1?

Thx Steven - as usual exactly the right answer to the question. I however have realised I'm asking completely the wrong question. What I in fact want to do is to create on the fly a nullary function object which returns a constant value. Possibly this is what lambda::constant does? Thx, Rob.

On Wednesday 01 December 2010 01:00:42 Robert Jones wrote:

I however have realised I'm asking completely the wrong question. What I in fact want to do is to create on the fly a nullary function object which returns a constant value.

Possibly this is what lambda::constant does?

lambda::constant or phoenix::val. Ravi

On Tue, Nov 30, 2010 at 11:48 PM, John B. Turpish wrote:

On Tue, Nov 30, 2010 at 10:06 AM, Robert Jones wrote:

...

Something that just returns it's single argument, eg.,

template <typename T> T identity( T t ) { return t; } ... (I need this because I need to pass a function object which simply returns an object I already have - maybe I've missed a more obvious method?)

The way you wrote it, wouldn't that actually return a temporary that is a copy of the object you already have? (rather than a const T& or something)

It would, (it was off-the-cuff for illustration) but also because my T type is in fact a pointer so copy semantics would be ok. Good point tho'. I have also realised I'm actually asking completely the wrong question in any case, so it's all become a bit irrelevant! Thx, Rob.