Re: [Boost-users] mpl documentation question

Steven Watanabe wrote:

AMDG

On 04/07/2012 10:47 AM, Robert Ramey wrote:

...

Vicente J. Botet Escriba wrote:

...

Le 07/04/12 09:13, Robert Ramey a écrit :

...

Documentation for mpl::less<T> has the following section:

typedef less r; // a

Return type:Integral Constant. Semantics:Equivalent to struct r : less::type {}; //b

if //a is used then the following yields bool_<true>

is_same< less, r>

if // b is used then the following yields bool_<false>

is_same< less, r>

So in what sense are //a and // b equivalent?

<snip> So you agree that the statement above (which appears in the documentation)

...

...

typedef less r; // a

Return type:Integral Constant. Semantics:Equivalent to struct r : less::type {}; //b

is incorrect and misleading?

I'm thinking that it shouldn't even be in the documentation as written. This raises the question as to what the documentation should say about the type "less" ?

is_same doesn't work, but what you can use is mpl::equal_to. mpl::equal_to compares integral constants for equality without requiring the types to match exactly:

equal_to, r> -> mpl::true_

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. 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.

In Christ, Steven Watanabe