[boost] Re: string algorithms review

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-23 14:10:52

Pavol Droba <droba_at_[hidden]> writes:

> On Thu, Oct 23, 2003 at 12:54:53PM -0400, David Abrahams wrote:
>> Pavol Droba <droba_at_[hidden]> writes:
>> 
>> > On Thu, Oct 23, 2003 at 09:42:35AM -0400, David Abrahams wrote:
>> >> Daniel Frey <daniel.frey_at_[hidden]> writes:
>> >> 
>> >> >  From a convenience POV, I would still prefer the copy-version to not
>> >> >  have a suffix, but that's probably just a matter of taste. My main
>> >> >  concern was safe use which is now addressed. Thanks.
>> >> 
>> >> My taste agrees.  The safer version should also be the more convenient
>> >> one.
>> >> 
>> > If the inplace variant returns void, it could not be misused. So it
>> > is safe too.
>> 
>> Mutating in-place, regardless of the return type, is less safe than
>> making a new copy of the data.  It's one of the basic principles of
>> functional programming, and why my coding guidelines recommend making
>> as many things const as possible, including function arguments.
>> 
>>    int f(int x)
>>    {
>>       if (condition) { ...
>>          modify(x);
>>       }
>>       ...
>> 
>>       int y = x + 3; // whoops, I forgot that x was modified
>>    }
>>            
>
> I understand very well the pronciples of functional programming. But
> functional language execute the program in totaly different way then
> imperative like C++.

C++ is a multiparadigm language.  Many of us like to do functional
programming in C++.  See Boost.Spirit/Phoenix, Boost.Bind,
Boost.Lambda, FC++, Boost.MPL, ...

> In C++ making a copy means a considerable overhead, in functional languages, 
> no copy is created, rather a term is reduced. 

?? We're not talking about making a copy, since the result differs
from the input.  In general, you pay the same price in functional
languages.

> So although I agree with you, that functional approach is more
> sound, in performance oriented imperative languages like C++ 

Whether or not C++ is "performance oriented" really depends how you
want to use it.

> it is not always the best approach.

Sure, it's not always the best approach.  It's still the safer
approach, and I prefer the safer approach to be more convenient.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com