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2805. void and reference type alternatives in variant, variant<> and index()

Section: 22.6 [variant], 22.6.3 [variant.variant], 22.6.3.2 [variant.ctor] Status: Resolved Submitter: Switzerland Opened: 2016-11-10 Last modified: 2020-09-06

Priority: Not Prioritized

View all issues with Resolved status.

Discussion:

Addresses CH 3, CH 4, CH 5, CH 6, CH 8

  1. variant allows reference types as alternatives; optional explicitly forbids to be instantiated for reference types. This is inconsistent.

  2. variant<int, void> should be as usable as variant<int>.

  3. variant<> should not have an index() function.

  4. Clarify the intended behavior of variant for alternative types that are references.

  5. Clarify variant construction.

Proposed change:

  1. Consider allowing reference types for both or none.

  2. —

  3. Consider specifying a specialization for variant<> like:

    template<> 
class variant<> 
{ 
public: 
  variant() = delete; 
  variant(const variant&) = delete; 
  variant& operator=(variant const&) = delete;
};

  4. Add a respective note.

  5. Add a note that variant<> cannot be constructed.

[Issues Telecon 16-Dec-2016]

Resolved by the adoption of P0501R0.

Proposed resolution: