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From: "matt at godbolt dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/52026] [c++0x] Constexpr Variable Appears Uninitialized in Lambda
Date: Tue, 29 Jan 2013 13:31:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

Matt Godbolt <matt at godbolt dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matt at godbolt dot org

--- Comment #10 from Matt Godbolt <matt at godbolt dot org> 2013-01-29 13:31:01 UTC ---
I have a smaller reproduction case, and some extra information:

References to non-explicitly captured constant values in template functions
generate invalid code.

An empty capture list fails to error, and generates invalid code.  A catch-all
capture list ([=] or [&]) correctly compiles, but generates invalid code.

A capture list that explicitly captures the constant value by reference or
value compiles and generates correct code.

With -Wall -Wextra, the constant is flagged as "uninitialized".

The code compiles and works correctly on GCC 4.5.2, but fails on GCC 4.6.3 and
GCC 4.7.2.

template<bool B>
int func() {
  const int constVal = B ? 100 : -100;
  return [] { return constVal; }();
}

int main(int, const char* []) {
  return func<true>();  // Returns 100 in -O0, but 0 in -O1 and above
}