Re: [boost] What is wrong with iterator macros?

From: Jeremy Siek (jsiek_at_[hidden])
Date: 2000-12-07 11:41:32

There's several problems:
  - if the compiler doesn't respect for-loop scoping,
   then if "i" is also defined in the enclosing scope
   there will be a problem, and because of the macro,
   someone may not realize that "int i" is being defined.

  - using "int" is typically a bad idea. The "n" is
  probably from the size() of some container, and therefore
  should have type "size_type". Comparing "int" with
  "size_type" in "i < n" will give warnings about comparing
  signed and unsigned integers. So "i" ought
  to be the "size_type" for the container.

  - the main purpose of code is communication... not
  between you and the machine, but between you and other
  programmers. Such macros obscure the meaning of
  the code.

On Thu, 7 Dec 2000 rwgk_at_[hidden] wrote:

> On request of David Abrahams I removed my beloved iterator
> macros from a few 'getting started' examples that I wrote
> for the Boost Python Library.
> 
> Here is what I normally use:
> 
> #ifndef DEFINE_RANGE_H
> #define DEFINE_RANGE_H
> 
> #define rangei(n)          for (int i = 0; i < n; i++)
> #define range1(i, n)       for (int i = 0; i < n; i++)
> #define range2(i, f, n)    for (int i = f; i < n; i++)
> #define range3(i, f, n, s) for (int i = f; i < n; i += s)
> 
> #endif // DEFINE_RANGE_H
> 
> This simple include file allows me to make my source code
> look a lot more concise. What is bad with this approach?
> Is it just "bad style" (why?), or are there more fundamental
> (i.e. real) problems?
> 
> This is probably not the most important question in the world,
> but each time I see myself typing (for int i = 0; i < 3; i++)
> I keep saying to myself that there must be a better way of
> doing this...
> 
> Ralf
> 
> 
> 
> 
> 
> 

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 Jeremy Siek                        www: http://www.lsc.nd.edu/~jsiek/
 Ph.D. Candidate                  email: jsiek_at_[hidden]
 Univ. of Notre Dame         work phone: [phone]
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