Add string StartsWith

Author: wilhuff

Firestore/core/src/firebase/firestore/util/string_util.cc

@@ -48,6 +48,11 @@ std::string ImmediateSuccessor(absl::string_view s) {
   return out;
 }
 
+bool StartsWith(const std::string &value, const std::string &prefix) {
+  return prefix.size() <= value.size() &&
+         std::equal(prefix.begin(), prefix.end(), value.begin());
+}
+
 }  // namespace util
 }  // namespace firestore
 }  // namespace firebase

Firestore/core/src/firebase/firestore/util/string_util.h

@@ -32,7 +32,7 @@ namespace firebase {
 namespace firestore {
 namespace util {
 
-/*
+/**
  * Returns the smallest lexicographically larger string of equal or smaller
  * length. Returns an empty string if there is no such successor (if the input
  * is empty or consists entirely of 0xff bytes).
@@ -44,7 +44,7 @@ namespace util {
  */
 std::string PrefixSuccessor(absl::string_view prefix);
 
-/*
+/**
  * Returns the immediate lexicographically-following string. This is useful to
  * turn an inclusive range into something that can be used with Bigtable's
  * SetLimitRow():
@@ -65,6 +65,11 @@ std::string PrefixSuccessor(absl::string_view prefix);
  */
 std::string ImmediateSuccessor(absl::string_view s);
 
+/**
+ * Returns true if the given value starts with the given prefix.
+ */
+bool StartsWith(const std::string &value, const std::string &prefix);
+
 }  // namespace util
 }  // namespace firestore
 }  // namespace firebase