"Vesa Karvonen" <vesa_karvonen@hotmail.com> writes:
I agree that the comment should be removed. I think that the comment has probably been more relevant at some stage (CVS would probably reveal it if this was the case), but the context was lost during editing. That ''BOOST_PP_DEC(I) essentially expands to "I-1"'' is hardly an implementation detail.
Well, it isn't correct, either. BOOST_PP_DEC(3) doesn't expand to "3-1"; it expands to 2
Is this really better than iterating over a SEQ of categories in any way other than efficiency?
At the time when the example was written, SEQ had not yet been invented and even lists were not as efficient and convenient as they are today. Unfortunately, the example was never updated. Today, I would generally advocate using a sequence (or some other data structure).
So that example should be stricken.
Example - Use BOOST_PP_REPEAT to avoid O(n*n) repetition.
It's unclear to me how that example avoids O(n*n) repetition.
The point is to avoid manual, source code time, repetition and replace it with automated, preprocessing time, repetition. The code that you will edit after using REPEAT will be only O(1) (and not O(n*n)).
It is the same as using a high level language to avoid programming in machine language. Sure, the compiler translates the high level code to machine language (well, not exactly, but close enough), but this doesn't mean that (because of the translation) you would not be avoiding programming in machine language as you seem to suggest.
No, I'm just suggesting that it's unclear what you mean when you write "avoid O(n*n) repetition". I took it to mean "avoid an inefficient use of the preprocessor resulting in O(n^2) complexity".
Example: Use arithmetic, logical, and comparison operations when necessary.
With no commentary, and no generated code, this example is really useless. I mean, of course you'd use arithmetic, logical, and comparison operations "when neccessary".
Looking at an old [...], there used to be a comment:
"<P>The PREPROCESSOR library supports saturated arithmetic, logical and comparison operations on decimal integer literals in the range [0,BOOST_PP_LIMIT_MAG].</p>
<p>Suppose that you want to generate a numbered lists with a special element inserted at a desired position. For example: E0, E1, S, E2. Consider the following example:</p>"
Putting it back would help.
The point of the example was really just to let the reader know that the library does contain macros for arithmetic, logic, etc...
The example is admittedly weak and only designed to use some of the mentioned classes of macros.
I think there should also be something that draws the distinction between BOOST_PP_ADD(4,7) and 4+7 and explains why you sometimes need the former. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com