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### 440. Should std::complex use unqualified transcendentals?

Section: 26.4.9 [complex.transcendentals] Status: NAD Submitter: Matt Austern Opened: 2003-11-05 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Operations like `pow` and `exp` on `complex<T>` are typically implemented in terms of operations like `sin` and `cos` on `T`. Should implementations write this as `std::sin`, or as plain unqualified `sin`?

The issue, of course, is whether we want to use argument-dependent lookup in the case where `T` is a user-defined type. This is similar to the issue of valarray transcendentals, as discussed in issue 226.

This issue differs from valarray transcendentals in two important ways. First, "the effect of instantiating the template `complex` for types other than float, double or long double is unspecified." (26.4.2 [complex.syn]) Second, the standard does not dictate implementation, so there is no guarantee that a particular real math function is used in the implementation of a particular complex function.

Proposed resolution:

Rationale:

If you instantiate std::complex for user-defined types, all bets are off.