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353.std::pair missing template assignment
Section: 22.3 [pairs] Status: Resolved Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
The class template std::pair defines a template ctor (20.2.2, p4) but no template assignment operator. This may lead to inefficient code since assigning an object of pair<C, D> to pair<A, B> where the types C and D are distinct from but convertible to A and B, respectively, results in a call to the template copy ctor to construct an unnamed temporary of type pair<A, B> followed by an ordinary (perhaps implicitly defined) assignment operator, instead of just a straight assignment.
Proposed resolution:
Add the following declaration to the definition of std::pair:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
And also add a paragraph describing the effects of the function template to the end of 20.2.2:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
Effects: first = p.first; second = p.second; Returns: *this
[Curaçao: There is no indication this is was anything other than a design decision, and thus NAD. May be appropriate for a future standard.]
[ Pre Bellevue: It was recognized that this was taken care of by N1856, and thus moved from NAD Future to NAD Editorial Resolved. ]
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