[llvm-bugs] [Bug 34664] New: variant uses "unsigned int" to store index, making it bigger than necessary

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https://bugs.llvm.org/show_bug.cgi?id=34664

            Bug ID: 34664
           Summary: variant uses "unsigned int" to store index, making it
                    bigger than necessary
           Product: libc++
           Version: 5.0
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: jonathan.sauer at gmx.de
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

In the following program, the size of "v" could be 2 (1 byte for the char, 1
byte for the index). Instead it is 8:

#include <variant>

using v = std::variant<char>;

static_assert(sizeof(v) == 8);


This is because currently variant stores its index as an unsigned int even when
a smaller type would suffice, wasting a fair amount of memory.

variant should use the smallest possible integer type to store its index.

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