Boost C++ Libraries: Ticket #4427: for_each does not take a non-const Function object

status changed; resolution set

anonymous — Fri, 13 Aug 2010 16:01:47 GMT

status new → closed
resolution → invalid

not a bug. to modify data in F, use a function object that holds a reference to mutable data.

anonymous — Wed, 13 Jun 2012 12:45:27 GMT

Replying to anonymous:

not a bug. to modify data in F, use a function object that holds a reference to mutable data.

Really? How is this solution better than accepting a non-const version of the operator?

status changed; resolution deleted

anonymous — Wed, 13 Jun 2012 12:48:43 GMT

status closed → reopened
resolution invalid

status changed; resolution set

Joel de Guzman — Wed, 13 Jun 2012 23:32:43 GMT

status reopened → closed
resolution → fixed

FYI, the newer version adds the non-const overload. Please check again. Yep, it was added due to popular demand.

status changed; resolution deleted

Joel de Guzman — Wed, 13 Jun 2012 23:38:24 GMT

status closed → reopened
resolution fixed

Reopening. It seems that the non-const overload has been there for some time now, so my comment above may be bogus. Please check it and provide a minimal test case if necessary (if it's not yet fixed). Pardon the potential confusion.

Joel de Guzman — Wed, 13 Jun 2012 23:56:40 GMT

And indeed my comments were all bogus. Please ignore. I realize now that this is about adding a non-const overload for function object, not the sequence (which has been there for a long time now).

So, indeed it still stands as -not-a-bug-. See the documentation: http://tinyurl.com/7uxyovh It is clear there that you can't expect F to be mutable. F can be passed around by value and any changes there will not update the actual F you passed in. Even STL algorithms are designed that way, so I am not sure why you are surprised (e.g. http://en.cppreference.com/w/cpp/algorithm/for_each; notice UnaryFunction f)

anonymous — Fri, 24 May 2013 18:03:35 GMT

The documentation does indicate a function object "F f", but the implementation (in 1.53) takes "F const&". So if no copy of the function object is made (and I can't see why it should), it seems:

The documentation should be corrected.
Given that no copy is necessary, why not accept a non-const "F& f" argument?

anonymous — Mon, 04 Nov 2013 11:13:10 GMT

Replying to djowel:

F can be passed around by value and any changes there will not update the actual F you passed in.

F can be wrapped in std::ref and any changes there will update the actual F.

Even STL algorithms are designed that way, so I am not sure why you are surprised (e.g. http://en.cppreference.com/w/cpp/algorithm/for_each; notice UnaryFunction f)

Notice, that f is passed by value, but not const reference.

anonymous — Wed, 20 Jun 2018 12:56:52 GMT

I was wondering whether there's been any news on this? Even with the 1.67 boost version, for_each cannot take a non-cost F...

owner, status changed

Joel de Guzman — Wed, 20 Jun 2018 21:40:51 GMT

owner changed from Joel de Guzman to Kohei Takahashi
status reopened → new

status, milestone changed; resolution set

Kohei Takahashi — Tue, 03 Jul 2018 03:41:53 GMT

status new → closed
resolution → fixed
milestone Boost 1.44.0 → To Be Determined

https://github.com/boostorg/fusion/pull/183

milestone changed

Kohei Takahashi — Wed, 04 Jul 2018 01:46:08 GMT

milestone To Be Determined → Boost 1.68.0