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Section: 29.5.2 [time.duration.cons] Status: C++11 Submitter: Howard Hinnant Opened: 2009-01-21 Last modified: 2016-01-28
Priority: Not Prioritized
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The following code should not compile because it involves implicit truncation errors (against the design philosophy of the duration library).
duration<double> d(3.5); duration<int> i = d; // implicit truncation, should not compile
This intent was codified in the example implementation which drove this proposal but I failed to accurately translate the code into the specification in this regard.
[ Batavia (2009-05): ]
We agree with the proposed resolution.
Move to Tentatively Ready.
[ 2009-07 Frankfurt ]
Moved from Tentatively Ready to Open only because the wording needs to be improved for enable_if type constraining, possibly following Robert's formula.
[ 2009-08-01 Howard adds: ]
Addressed by 1177.
[ 2009-10 Santa Cruz: ]
Not completely addressed by 1177. Move to Ready.
Change 29.5.2 [time.duration.cons], p4:
template <class Rep2, class Period2> duration(const duration<Rep2, Period2>& d);
-4- Requires: treat_as_floating_point<rep>::value shall be true or ratio_divide<Period2, period>::type::den shall be 1 . Diagnostic required. [Note: This requirement prevents implicit truncation error when converting between integral-based duration types. Such a construction could easily lead to confusion about the value of the duration. — end note]