Port comparison to C++ (#678)

This reimplements our comparison functions as C++ Comparators and then provides compatibility shims for interoperating with existing Objective-C usage.

A few specialized comparators aren't suitable for porting but only have a single usage (e.g. CompareBytes for comparing NSData * instances). In these cases I've moved them into the caller.

* Use int32_t for typeof(ID) in FSTDocumentReference

* Migrate callers of FSTComparison.h to Objective-C++

* Port comparison to C++

* Migrate usages of FSTComparison.h to C++ equivalents

* Remove FSTComparison

1 files changed, 13 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/util/string_apple.h b/Firestore/core/src/firebase/firestore/util/string_apple.h
index e1be8c3..108ade7 100644
--- a/Firestore/core/src/firebase/firestore/util/string_apple.h
+++ b/Firestore/core/src/firebase/firestore/util/string_apple.h
@@ -17,8 +17,13 @@
 #ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_APPLE_H_
 #define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_APPLE_H_
 
+// Everything in this header exists for compatibility with Objective-C.
+#if __OBJC__
+
 #import <Foundation/Foundation.h>
 
+#include "absl/strings/string_view.h"
+
 namespace firebase {
 namespace firestore {
 namespace util {
@@ -32,8 +37,16 @@ inline NSString* WrapNSStringNoCopy(const char* c_str) {
              freeWhenDone:NO];
 }
 
+// Creates an absl::string_view wrapper for the contents of the given NSString.
+inline absl::string_view MakeStringView(NSString* str) {
+  return absl::string_view(
+      [str UTF8String], [str lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
+}
+
 }  // namespace util
 }  // namespace firestore
 }  // namespace firebase
 
+#endif  // __OBJC__
+
 #endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_APPLE_H_