Is it wrong to describe for_each as a modifying algorithm? It is
described as one here: http://www.josuttis.com/libbook/algolist.pdf.
transform appears to be the algorithm to use for modifying elements in a
range.
Fraser.
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"Fraser Ross" <fraserATmember s.v21.co.ukwrot e:
Is it wrong to describe for_each as a modifying algorithm? It is
described as one here: http://www.josuttis.com/libbook/algolist.pdf.
transform appears to be the algorithm to use for modifying elements in a
range.
for_each is a non-modifying algorithm does not explicitly modify the
contents of the container. The functor passed into for_each might, but
the algorithm doesn't. Specifically, there is no assignment operation
inside the algorithm.
--
There are two things that simply cannot be doubted. Logic and our
ability to sense the world around us. Doubt those, and you no longer
have anyone to discuss it with, nor any ability to discuss it.
"Daniel T."
for_each is a non-modifying algorithm does not explicitly modify the
contents of the container. The functor passed into for_each might, but
the algorithm doesn't.
I think the intention is that although the algorithm doesn't prevent
modification it is expected anyway that the functor does not modify
elements.
Fraser.
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In article <11************ **@sp6iad.super feed.net>, "Fraser Ross"
<fraserATmember s.v21.co.uksays ...
Is it wrong to describe for_each as a modifying algorithm? It is
described as one here: http://www.josuttis.com/libbook/algolist.pdf.
transform appears to be the algorithm to use for modifying elements in a
range.
The C++ standard places the description of for_each in the "Non-
modifying Sequence Operations." OTOH, there's nothing in its description
that precludes it from modifying the items in the sequence either.
--
Later,
Jerry.
The universe is a figment of its own imagination.
In article <11************ **@sp6iad.super feed.net>, "Fraser Ross"
<fraserATmember s.v21.co.uksays ...
>
"Daniel T."
for_each is a non-modifying algorithm does not explicitly modify the
contents of the container. The functor passed into for_each might, but
the algorithm doesn't.
I think the intention is that although the algorithm doesn't prevent
modification it is expected anyway that the functor does not modify
elements.
I doubt it. Other algorithms (e.g. transform) state specific
requirements about lack of side-effects in the operations they invoke. I
think if that was intended, it would be stated in the dsecription of
for_each as well.
--
Later,
Jerry.
The universe is a figment of its own imagination.
"Fraser Ross" <fraserATmember s.v21.co.ukwrot e:
>
"Daniel T."
>for_each is a non-modifying algorithm does not explicitly modify the
contents of the container. The functor passed into for_each might, but
the algorithm doesn't.
I think the intention is that although the algorithm doesn't prevent
modification it is expected anyway that the functor does not modify
elements.
That intention is not stated in the standard. The description of for_each is
very clear:
template<class InputIterator, class Function>
Function for_each(InputI terator first, InputIterator last, Function f);
Effects: Applies f to the result of dereferencing every iterator in the
range [first, last), starting from first and proceeding to last - 1.
Returns: f.
Complexity: Applies f exactly last - first times.
It follows that if you pass a const_iterator, you will not be able to
modify. If you pass a (non-const) iterator, you will be able to modify
because the result of dereferencing the iterator is not const.
Best
Kai-Uwe Bux
The book "STL Tutorial And Reference Guide" says "It is assumed f does
not apply any nonconstant function through the dereferenced iterator."
The help files with BCB6 says "Since this a non-mutating algorithm, the
function f cannot make any modifications to the sequence, but it can
achieve results through side effects (such as copying or printing). "
They seem to expecting the range to not be modified.
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"Fraser Ross" <fraserATmember s.v21.co.ukwrot e:
The book "STL Tutorial And Reference Guide" says "It is assumed f does
not apply any nonconstant function through the dereferenced iterator."
The help files with BCB6 says "Since this a non-mutating algorithm, the
function f cannot make any modifications to the sequence, but it can
achieve results through side effects (such as copying or printing). "
They seem to expecting the range to not be modified.
As I already pointed out, those opinions have, to the best of my knowledge,
no basis in the language of the standard. Maybe you should ask the authors
of your sources, where in the standard they find the provisions in support
for their theory.
Best
Kai-Uwe Bux
Fraser Ross wrote:
The book "STL Tutorial And Reference Guide" says "It is assumed f does
not apply any nonconstant function through the dereferenced iterator."
The help files with BCB6 says "Since this a non-mutating algorithm, the
function f cannot make any modifications to the sequence, but it can
achieve results through side effects (such as copying or printing). "
They seem to expecting the range to not be modified.
On the other hand, if you look at the page cited in the original
message, it lists for_each as both a non-modifying algorithm and a
modifying algorithm.
Much of this confusion comes from failing to distinguish between two
different modifications: modifying the order of the elements in the
passed sequence (e.g. sort) and modifying elements in the sequence (e.g.
transform).
In fact, the classification in the standard distinguishes between
modifying sequence operations and non-modifying sequence operations. The
choice of words is deliberate: it emphasizes that what's being operated
on is the sequence, and not the elements themselves. So for_each is a
non-modifying sequence operation, because it does not modify the order
the elements in the sequence.
There's a newly added note that says that if you pass a mutable iterator
to for_each, the function can modify the elements.
--
-- Pete
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see www.petebecker.com/tr1book.
In article <11************ **@sp6iad.super feed.net>,
"Fraser Ross" <fraserATmember s.v21.co.ukwrot e:
The book "STL Tutorial And Reference Guide" says "It is assumed f does
not apply any nonconstant function through the dereferenced iterator."
The help files with BCB6 says "Since this a non-mutating algorithm, the
function f cannot make any modifications to the sequence, but it can
achieve results through side effects (such as copying or printing). "
They seem to expecting the range to not be modified.
From Stroustrup:
The for_each() algorithm is classified as nonmodifying because it
doesn't explicitly modify a sequence. However, if applied to a
non-const sequence for_each()'s operation (its third argument) may
change the elements of the sequence.
--
There are two things that simply cannot be doubted. Logic and our
ability to sense the world around us. Doubt those, and you no longer
have anyone to discuss it with, nor any ability to discuss it. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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last post by:
Functor-parameters in the for_each() and transform() algorithms are passed by value.
Might it make sense to have also algorithms for_each2() and transform2()
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Here is some program which demonstrates probable necessity
in such forms of for_each() and transform().
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Hello,
I'm new in this group and I don't know if my questions are too silly,
but I'm intermediate programmer and don't have enought experience.
Please be charitable.
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Maybe example will be more accurate:
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