Re: [Boost-users] mpl documentation question

Subject: Re: [Boost-users] mpl documentation question
From: Robert Ramey (ramey_at_[hidden])
Date: 2012-04-07 15:32:31

Steven Watanabe wrote:
> AMDG
>
> On 04/07/2012 12:05 PM, Robert Ramey wrote:
>>
>> That's interesting and useful.  So I guess my problem is with the
>> usage
>> of the term "equivalent".  I had interpreted this as "can be
>> substituted for".
>>
>> So I'm now thinking that my original concern is justified - that the
>> document
>> doesn't accurately convey what "less<c1, c2>" really is.
>
> Yes.  I agree that the documentation needs
> some work here.
>
>>  This has always
>> been confusing to me - and still is. I totally get what "less<c1,
>> c2>::type" is
>> supposed to mean but the meaning and intended usage of "less<c1, c2>"
>> is still lost on me.
>>
>
> Okay, I'll try to explain more clearly.
> mpl::less<c1, c2>::type is the result of invoking
> the metafunction.  This is the way all metafunctions
> work in MPL so no surprises here.
>
> Now, mpl::less<c1, c2> is itself an MPL Integral
> Constant.  This works because MPL Integral Constant
> is a Concept rather than a specific template.
> In other words, if you only care about
> the *value* of the result, and not the *exact type*,
> then you can use mpl::less<c1, c2> instead of
> typename mpl::less<c1, c2>::type.  Just think
> of this as a convenient short-cut for arithmetic
> metafunctions.
>
> In Christ,
> Steven Watanabe

great answer - next time you come up to Santa Barbara, give me a call,  I'll 
buy you lunch.

Robert Ramey