Mojo: Add support for converting between mojo::String and base::StringPiece.

This CL also adds an implicit conversion operator to type U that works
just like an explicit call to To<U>. This is to go along with the implicit
conversion constructors on mojo::Array and generated class types. While
discouraged by the style guide, I think this kind of implicit conversion
will be very helpful at reducing code verbosity. It shouldn't be too
dangerous either.

Finally, I took this opportunity to de-inline specializations of
SimilarityTraits where possible.

BUG=324594

Review URL: https://codereview.chromium.org/98313002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238085 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 65 insertions, 19 deletions

diff --git a/mojo/public/bindings/generators/cpp_templates/wrapper_class_declaration b/mojo/public/bindings/generators/cpp_templates/wrapper_class_declaration
index f399ddf..402039c 100644
--- a/mojo/public/bindings/generators/cpp_templates/wrapper_class_declaration
+++ b/mojo/public/bindings/generators/cpp_templates/wrapper_class_declaration
@@ -18,6 +18,11 @@ class $CLASS {
   }
 
   template <typename U>
+  operator U() const {
+    return To<U>();
+  }
+
+  template <typename U>
   U To() const {
     return mojo::SimilarityTraits<$CLASS,U>::CopyTo(*this);
   }
diff --git a/mojo/public/bindings/lib/bindings.cc b/mojo/public/bindings/lib/bindings.cc
new file mode 100644
index 0000000..9f4d6fd
--- /dev/null
+++ b/mojo/public/bindings/lib/bindings.cc
@@ -0,0 +1,31 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/public/bindings/lib/bindings.h"
+
+namespace mojo {
+
+// static
+String SimilarityTraits<String, std::string>::CopyFrom(const std::string& input,
+                                                       Buffer* buf) {
+  String::Builder result(input.size(), buf);
+  memcpy(&result[0], input.data(), input.size());
+  return result.Finish();
+}
+// static
+std::string SimilarityTraits<String, std::string>::CopyTo(const String& input) {
+  return input.is_null() ? std::string() :
+                           std::string(&input[0], &input[0] + input.size());
+}
+
+// static
+String SimilarityTraits<String, const char*>::CopyFrom(const char* input,
+                                                       Buffer* buf) {
+  size_t size = strlen(input);
+  String::Builder result(size, buf);
+  memcpy(&result[0], input, size);
+  return result.Finish();
+}
+
+}  // namespace mojo
diff --git a/mojo/public/bindings/lib/bindings.h b/mojo/public/bindings/lib/bindings.h
index 3992ccf..db1c092 100644
--- a/mojo/public/bindings/lib/bindings.h
+++ b/mojo/public/bindings/lib/bindings.h
@@ -39,6 +39,11 @@ class Array {
   }
 
   template <typename U>
+  operator U() const {
+    return To<U>();
+  }
+
+  template <typename U>
   U To() const {
     return SimilarityTraits<Array<T>,U>::CopyTo(*this);
   }
@@ -95,14 +100,8 @@ typedef Array<char> String;
 template <>
 class SimilarityTraits<String, std::string> {
  public:
-  static String CopyFrom(const std::string& input, Buffer* buf) {
-    String::Builder result(input.size(), buf);
-    memcpy(&result[0], input.data(), input.size());
-    return result.Finish();
-  }
-  static std::string CopyTo(const String& input) {
-    return std::string(&input[0], &input[0] + input.size());
-  }
+  static String CopyFrom(const std::string& input, Buffer* buf);
+  static std::string CopyTo(const String& input);
 };
 
 template <size_t N>
@@ -127,12 +126,7 @@ class SimilarityTraits<String, const char[N]> {
 template <>
 class SimilarityTraits<String, const char*> {
  public:
-  static String CopyFrom(const char* input, Buffer* buf) {
-    size_t size = strlen(input);
-    String::Builder result(size, buf);
-    memcpy(&result[0], input, size);
-    return result.Finish();
-  }
+  static String CopyFrom(const char* input, Buffer* buf);
   // NOTE: |CopyTo| explicitly not implemented since String is not null
   // terminated (and may have embedded null bytes).
 };
@@ -147,14 +141,16 @@ class SimilarityTraits<Array<T>, std::vector<E> > {
     return result.Finish();
   }
   static std::vector<E> CopyTo(const Array<T>& input) {
-    std::vector<E> result(input.size());
-    for (size_t i = 0; i < input.size(); ++i)
-      result[i] = SimilarityTraits<T, E>::CopyTo(input[i]);
+    std::vector<E> result;
+    if (!input.is_null()) {
+      result.resize(input.size());
+      for (size_t i = 0; i < input.size(); ++i)
+        result[i] = SimilarityTraits<T, E>::CopyTo(input[i]);
+    }
     return result;
   }
 };
 
-
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_H_
diff --git a/mojo/public/tests/bindings_type_conversion_unittest.cc b/mojo/public/tests/bindings_type_conversion_unittest.cc
index 0c4a870..01050fa 100644
--- a/mojo/public/tests/bindings_type_conversion_unittest.cc
+++ b/mojo/public/tests/bindings_type_conversion_unittest.cc
@@ -83,6 +83,11 @@ TEST_F(BindingsTypeConversionTest, String) {
   EXPECT_EQ(std::string(kText), c.To<std::string>());
 }
 
+TEST_F(BindingsTypeConversionTest, String_Null) {
+  String a;
+  EXPECT_EQ(std::string(), a.To<std::string>());
+}
+
 TEST_F(BindingsTypeConversionTest, String_ShallowCopy) {
   AllocationScope scope;
 
@@ -129,6 +134,15 @@ TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits) {
   EXPECT_EQ(rect.height(), rect2.height());
 }
 
+TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits_Array_Null) {
+  Array<test_structs::Rect> rects;
+
+  std::vector<RedmondRect> redmond_rects =
+      rects.To<std::vector<RedmondRect> >();
+
+  EXPECT_TRUE(redmond_rects.empty());
+}
+
 TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits_Array) {
   AllocationScope scope;
 
@@ -171,7 +185,7 @@ TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits_Array) {
   }
 }
 
-TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits_Array2) {
+TEST_F(BindingsTypeConversionTest, CustomSimilarityTraits_Nested) {
   AllocationScope scope;
 
   RedmondNamedRegion redmond_region;