Add output formatters for more mojom types.

mojo/public/cpp/bindings/formatting.h

Index: mojo/public/cpp/bindings/formatting.h
diff --git a/mojo/public/cpp/bindings/formatting.h b/mojo/public/cpp/bindings/formatting.h
new file mode 100644
index 0000000000000000000000000000000000000000..97b1aedc2894587384289484c99c1218da6da33a
--- /dev/null
+++ b/mojo/public/cpp/bindings/formatting.h
@@ -0,0 +1,77 @@
+// Copyright 2016 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.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_FORMATTING_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_FORMATTING_H_
+
+#include <iosfwd>
+
+#include "mojo/public/cpp/bindings/array.h"
+#include "mojo/public/cpp/bindings/map.h"
+#include "mojo/public/cpp/bindings/struct_ptr.h"
+
+namespace mojo {
+
+// Prints the contents of an array to an output stream in a human-readable
+// format.
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const mojo::Array<T>& array) {
+  if (array) {
+    os << "[";
+    bool first = true;
+    for (auto it = array.storage().cbegin(); it != array.storage().cend();
+         ++it) {
+      if (first)
+        first = false;
+      else
+        os << ", ";
+      os << *it;
+    }
+    os << "]";
+  } else {
+    os << "null";
+  }
+  return os;
+}
+
+// Prints the contents of a map to an output stream in a human-readable
+// format.
+template <typename Key, typename Value>

[viettrungluu, 2016/01/26 18:44:05]

This is maybe a bit bikesheddy, but I think that the world (JS/JSON, Python,
Dart, Go, ...) has mostly agreed to format maps as {key1: value1, key2: value2}
(with varying spacing/indentation).

[jeffbrown, 2016/01/26 22:57:59]

Done.

+std::ostream& operator<<(std::ostream& os, const mojo::Map<Key, Value>& map) {
+  if (map) {
+    os << "[";
+    bool first = true;
+    for (auto it = map.cbegin(); it != map.cend(); ++it) {
+      if (first)
+        first = false;
+      else
+        os << ", ";
+      os << "{" << it.GetKey() << ": " << it.GetValue() << "}";
+    }
+    os << "]";
+  } else {
+    os << "null";
+  }
+  return os;
+}
+
+// Prints the pointee of a Mojo structure pointer to an output stream
+// assuming there exists an operator<< overload that accepts a const
+// reference to the object.
+template <typename T, typename = typename T::Data_>
+auto operator<<(std::ostream& os, const T* value) -> decltype(os << *value) {
+  return value ? os << *value : os << "null";
+}
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const StructPtr<T>& value) {
+  return os << value.get();
+}
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const InlinedStructPtr<T>& value) {
+  return os << value.get();
+}
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_FORMATTING_H_