[C++14] Admit C++ keywords as literal suffixes.

[Ed Smith-Rowland]

I understand that the literal operators for complex numbers for C++14 
faltered at least in part because of the perceived ugliness of the float 
operator:

constexpr complex<float>
operator"" i_f();  //  fugly
The obvious choice
constexpr complex<float>
operator"" if();

failed because 'if' is a keyword.  The 'if' keyword can never be exposed 
in this context either by usage in a literal or by explicit call.

Allowing keywords as literal operator suffixes turns out to be a 6-liner 
if gcc.  I actually think *disallowing* them is a bit of a bug.  (Not 
sure if it was me or the standard).

I don't know if that's the wording but I just wanted to offer a working 
implementation of the idea.

Ed

Index: gcc/cp/parser.c
===================================================================
--- gcc/cp/parser.c     (revision 200158)
+++ gcc/cp/parser.c     (working copy)
@@ -12359,6 +12358,13 @@
              return cp_literal_operator_id (name);
            }
        }
+      else if (token->type == CPP_KEYWORD)
+       {
+         id = ridpointers [(int) token->keyword];
+         cp_lexer_consume_token (parser->lexer);
+         const char *name = IDENTIFIER_POINTER (id);
+         return cp_literal_operator_id (name);
+       }
       else
        {
          error ("expected suffix identifier");