# ============================================================================
#  http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_11.html
# ============================================================================
#
# SYNOPSIS
#
#   AX_CXX_COMPILE_STDCXX_11([ext|noext],[mandatory|optional])
#
# DESCRIPTION
#
#   Check for baseline language coverage in the compiler for the C++11
#   standard; if necessary, add switches to CXXFLAGS to enable support.
#
#   The first argument, if specified, indicates whether you insist on an
#   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
#   -std=c++11).  If neither is specified, you get whatever works, with
#   preference for an extended mode.
#
#   The second argument, if specified 'mandatory' or if left unspecified,
#   indicates that baseline C++11 support is required and that the macro
#   should error out if no mode with that support is found.  If specified
#   'optional', then configuration proceeds regardless, after defining
#   HAVE_CXX11 if and only if a supporting mode is found.
#
# LICENSE
#
#   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
#   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
#   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>
#
#   Copying and distribution of this file, with or without modification, are
#   permitted in any medium without royalty provided the copyright notice
#   and this notice are preserved. This file is offered as-is, without any
#   warranty.

#serial 3

m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody], [
  template <typename T>
    struct check
    {
      static_assert(sizeof(int) <= sizeof(T), "not big enough");
    };

    typedef check<check<bool>> right_angle_brackets;

    int a;
    decltype(a) b;

    typedef check<int> check_type;
    check_type c;
    check_type&& cr = static_cast<check_type&&>(c);

    auto d = a;
])

AC_DEFUN([AX_CXX_COMPILE_STDCXX_11], [dnl
  AC_ARG_WITH([c++11],
    AS_HELP_STRING(
        [--with-c++11=@<:@ARG@:>@],
        [use C++11 when available @<:@default=yes@:>@]
    ),
    [
    if test "$withval" = "no"; then
        WANT_CXX11="no"
    fi
    ],
    [WANT_CXX11="yes"]
  )

  if test "x$WANT_CXX11" = "xyes"; then
    m4_if([$1], [], [],
          [$1], [ext], [],
          [$1], [noext], [],
          [m4_fatal([invalid argument `$1' to AX_CXX_COMPILE_STDCXX_11])])dnl
    m4_if([$2], [], [ax_cxx_compile_cxx11_required=true],
          [$2], [mandatory], [ax_cxx_compile_cxx11_required=true],
          [$2], [optional], [ax_cxx_compile_cxx11_required=false],
          [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX_11])])dnl
    AC_LANG_PUSH([C++])dnl
    ac_success=no
    AC_CACHE_CHECK(whether $CXX supports C++11 features by default,
    ax_cv_cxx_compile_cxx11,
    [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
      [ax_cv_cxx_compile_cxx11=yes],
      [ax_cv_cxx_compile_cxx11=no])])
    if test x$ax_cv_cxx_compile_cxx11 = xyes; then
      ac_success=yes
    fi
    
    m4_if([$1], [noext], [], [dnl
    if test x$ac_success = xno; then
      for switch in -std=gnu++11 -std=gnu++0x; do
        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
        AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
                       $cachevar,
          [ac_save_CXXFLAGS="$CXXFLAGS"
           CXXFLAGS="$CXXFLAGS $switch"
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
            [eval $cachevar=yes],
            [eval $cachevar=no])
           CXXFLAGS="$ac_save_CXXFLAGS"])
        if eval test x\$$cachevar = xyes; then
          CXXFLAGS="$CXXFLAGS $switch"
          ac_success=yes
          break
        fi
      done
    fi])
    
    m4_if([$1], [ext], [], [dnl
    if test x$ac_success = xno; then
      for switch in -std=c++11 -std=c++0x; do
        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
        AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
                       $cachevar,
          [ac_save_CXXFLAGS="$CXXFLAGS"
           CXXFLAGS="$CXXFLAGS $switch"
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
            [eval $cachevar=yes],
            [eval $cachevar=no])
           CXXFLAGS="$ac_save_CXXFLAGS"])
        if eval test x\$$cachevar = xyes; then
          CXXFLAGS="$CXXFLAGS $switch"
          ac_success=yes
          break
        fi
      done
    fi])
    AC_LANG_POP([C++])
    if test x$ax_cxx_compile_cxx11_required = xtrue; then
      if test x$ac_success = xno; then
        AC_MSG_ERROR([*** A compiler with support for C++11 language features is required.])
      fi
    else
      if test x$ac_success = xno; then
        HAVE_CXX11=0
        AC_MSG_NOTICE([No compiler with C++11 support was found])
      else
        HAVE_CXX11=1
        AC_DEFINE(HAVE_CXX11,1,
                  [define if the compiler supports basic C++11 syntax])
      fi
    
      AC_SUBST(HAVE_CXX11)
    fi
  fi
])