remove constexpr since gcc 4.4 or vs2010 does not support it

include/grpc++/support/string_ref.h

@@ -50,22 +50,22 @@ class string_ref {
   typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
   // constants
-  static constexpr size_t npos = size_t(-1);
+  static size_t npos = size_t(-1);
 
   // construct/copy.
-  constexpr string_ref() : data_(nullptr), length_(0) {}
+  string_ref() : data_(nullptr), length_(0) {}
-  constexpr string_ref(const string_ref& other)
+  string_ref(const string_ref& other)
       : data_(other.data_), length_(other.length_) {}
   string_ref& operator=(const string_ref& rhs);
   string_ref(const char* s);
-  constexpr string_ref(const char* s, size_t l) : data_(s), length_(l) {}
+  string_ref(const char* s, size_t l) : data_(s), length_(l) {}
   string_ref(const grpc::string& s) : data_(s.data()), length_(s.length()) {}
 
   // iterators
-  constexpr const_iterator begin() const { return data_; }
+  const_iterator begin() const { return data_; }
-  constexpr const_iterator end() const { return data_ + length_; }
+  const_iterator end() const { return data_ + length_; }
-  constexpr const_iterator cbegin() const { return data_; }
+  const_iterator cbegin() const { return data_; }
-  constexpr const_iterator cend() const { return data_ + length_; }
+  const_iterator cend() const { return data_ + length_; }
   const_reverse_iterator rbegin() const {
     return const_reverse_iterator(end());
   }
@@ -80,10 +80,10 @@ class string_ref {
   }
 
   // capacity
-  constexpr size_t size() const { return length_; }
+  size_t size() const { return length_; }
-  constexpr size_t length() const { return length_; }
+  size_t length() const { return length_; }
-  constexpr size_t max_size() const { return length_; }
+  size_t max_size() const { return length_; }
-  constexpr bool empty() const { return length_ == 0; }
+  bool empty() const { return length_ == 0; }
 
   // element access
   const char* data() const { return data_; }
@@ -95,9 +95,7 @@ class string_ref {
   size_t find(string_ref s) const;
   size_t find(char c) const;
 
-  // Defined as constexpr in n3442 but C++11 constexpr semantics do not allow
+  string_ref substr(size_t pos, size_t n = npos) const;
-  // the implementation of this function to comply.
-  /* constrexpr */ string_ref substr(size_t pos, size_t n = npos) const;
 
  private:
   const char* data_;

src/cpp/util/string_ref.cc

@@ -39,7 +39,7 @@
 
 namespace grpc {
 
-constexpr size_t string_ref::npos;
+size_t string_ref::npos;
 
 string_ref& string_ref::operator=(const string_ref& rhs) {
   data_ = rhs.data_;