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