add SkVptr()

I was wondering how feasible using this to make downcasts safe would be.
These tests would need to build and pass on all our bots, at least.

Change-Id: I1753ba58841bf6c17d6ac3af7374518356e1bb05
Reviewed-on: https://skia-review.googlesource.com/81180
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/core/SkVptr.h b/src/core/SkVptr.h
new file mode 100644
index 0000000000..2a33ad06c7
--- /dev/null
+++ b/src/core/SkVptr.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkVptr_DEFINED
+#define SkVptr_DEFINED
+
+#include <string.h>
+#include <type_traits>
+
+// Experimentally, see if we can get at the vptr of objects with one.
+
+template <typename T>
+static inline void* SkVptr(const T& object) {
+    static_assert(std::has_virtual_destructor<T>::value, "");
+    void* vptr;
+    memcpy(&vptr, (const void*)&object, sizeof(vptr));
+    return vptr;
+}
+
+#endif//SkVptr_DEFINED