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1340. Why doesforward_list::resize take the object to be copied by value?

Section: 23.3.7.5[forward.list.modifiers]Status:C++11Submitter: James McNellisOpened: 2010-07-16Last modified: 2023-02-07

Priority:Not Prioritized

View all otherissues in [forward.list.modifiers].

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Discussion:

InN3092 [forwardlist.modifiers], theresize() member function is declared as:

void resize(size_type sz, value_type c);

The other sequence containers (list,deque, andvector) take'c' by const reference.

Is there a reason for this difference? If not, thenresize() should be declared as:

void resize(size_type sz, const value_type& c);

The declaration would need to be changed both at its declaration in the classdefinition at [forwardlist]/3 and where its behavior is specifiedat [forwardlist.modifiers]/22.

This would makeforward_list consistent with the CD1 issue679⁽ⁱ⁾.

[Post-Rapperswil]

Daniel changed the P/R slightly, because one paragraph number has been changed since the issuehad been submitted. He also added a similar Requires element that exists in all other containers witharesize member function. He deliberately did not touch the wrong usage of "default-constructed" because thatwill be taken care of by LWG issue868⁽ⁱ⁾.

Moved to Tentatively Ready with revised wording after 5 positive votes on c++std-lib.

[Adopted at 2010-11 Batavia]

Proposed resolution:

1. Change [forwardlist]/3, class templateforward_list synopsis, as indicated:

   ...void resize(size_type sz);void resize(size_type sz,const value_type& c);void clear();...

2. Change [forwardlist.modifiers]/27 as indicated:

   void resize(size_type sz);void resize(size_type sz,const value_type& c);

   27Effects: Ifsz < distance(begin(), end()), erases the lastdistance(begin(), end()) - sz elementsfrom the list. Otherwise, insertssz - distance(begin(), end()) elements at the end of the list. For the first signature the inserted elements are default constructed, and for the second signature they are copies ofc.

   28 -Requires:T shall beDefaultConstructible for the first form andit shall beCopyConstructible for the second form.