[llvm-bugs] [Bug 42602] New: Dereferencing an initilizer_list::begin() is not treated as a constant expression

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https://bugs.llvm.org/show_bug.cgi?id=42602

            Bug ID: 42602
           Summary: Dereferencing an initilizer_list::begin() is not
                    treated as a constant expression
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: antoshkka at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Following example does not compile in C++11 and later std modes:


#include <initializer_list>

constexpr std::initializer_list<unsigned> i_list = {10u};

unsigned test() {
    constexpr unsigned v = *i_list.begin();
    return v;
}


Errors:
<source>:6:24: error: constexpr variable 'v' must be initialized by a constant
expression
    constexpr unsigned v = *i_list.begin();

                       ^   ~~~~~~~~~~~~~~~
<source>:6:28: note: read of temporary is not allowed in a constant expression
outside the expression that created the temporary
    constexpr unsigned v = *i_list.begin();

                           ^
<source>:3:52: note: temporary created here
constexpr std::initializer_list<unsigned> i_list = {10u};

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