Re: [Boost-users] Re: [MPL] replace_if question

From: David Greene (greened_at_[hidden])
Date: 2004-12-23 13:27:27

David Abrahams wrote:

>>{
>>	replaceit<
>>		vector<
>>                     charm
> 
> 
> You should be seeing a syntax error right here.

:) I'll admit I had to patch something up in the e-mail.  Obviously
I mistyped.

>>What's the right way to do this?
> 
> Use an algorithm like transform that _computes_ the new values rather
> than simply replacing them with a constant value:

Ok, thanks.  I have to read some more to better understand which
algorithms operate on constants and which invoke metafunctions.
I should have been clued in by the name to look up the STL version.

>>Furthermore, is there a better way to identify pairs in
>>replace_if than deriving from a special class?  All I can
>>think of is writing a predicate class and specializing it
>>for mpl::pair<U, V>.  Seems like there should be an easier
>>way.
> 
> Why?  That seems like a pretty darned good approach to me.

I guess it didn't feel like the "mpl way" to me.  I remember
back when MPL was first being discussed that the STL-ness of
it was compared to the pattern-matching approach of Loki.  I
was a doubter about the STL-ness but now that I've used it
some I'm warming up to it.  :)

Thanks again.  I'm slowly climbing the curve...

                          -Dave