Re: [Boost-users] mpl documentation question

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" 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::type" is supposed to mean but the meaning and intended usage of "less" is still lost on me.

Okay, I'll try to explain more clearly. mpl::less::type is the result of invoking the metafunction. This is the way all metafunctions work in MPL so no surprises here.

Now, mpl::less 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 instead of typename mpl::less::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