Asymmetric lower_bound

Hi C++ experts,

In X86FloatingPoint.cpp there is a struct TableEntry that can be compared to an unsigned:

    friend bool operator<(const TableEntry &TE, unsigned V) {
      return TE.from < V;

This is used with std::lower_bound():

static int Lookup(const TableEntry *Table, unsigned N, unsigned Opcode) {
  const TableEntry *I = std::lower_bound(Table, Table+N, Opcode);

It looks like the GNU libstdc++ is happy with the asymmetric types in the comparison, but MSVC insists that the transposed operator< also be available:

    friend bool operator<(unsigned V, const TableEntry &TE) {
      return V < TE.from;

It is not really clear from the draft C++0x standard what is required when the comparison function takes asymmetric types.

Is MSVC wrong here, and lower_bound should work with only one asymmetric comparison available?
Is it a bug in the standard that it isn't clearly specified?


The LWG has consistently affirmed over the years that lower_bound and upper_bound tolerate asymmetric compares (but in opposite senses).

  lower_bound only requires:

     *j < value or comp(*j, value)

  upper_bound only requires:

     (value < *j) or comp(value, *j)



I guess we will have to keep the other operator< around for MSVC's sake.