SkPDF: use std::aligned_storage for typed union

Change-Id: I38e063cf7557aab1cffbaa126aea4dc7142d914c
Reviewed-on: https://skia-review.googlesource.com/121583
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

2 files changed, 23 insertions, 14 deletions

diff --git a/src/pdf/SkPDFTypes.cpp b/src/pdf/SkPDFTypes.cpp
index c1505ea413..3a8120995c 100644
--- a/src/pdf/SkPDFTypes.cpp
+++ b/src/pdf/SkPDFTypes.cpp
@@ -15,18 +15,13 @@
 
 ////////////////////////////////////////////////////////////////////////////////
 
-SkString* pun(char* x) { return reinterpret_cast<SkString*>(x); }
-const SkString* pun(const char* x) {
-    return reinterpret_cast<const SkString*>(x);
-}
-
 SkPDFUnion::SkPDFUnion(Type t) : fType(t) {}
 
 SkPDFUnion::~SkPDFUnion() {
     switch (fType) {
         case Type::kNameSkS:
         case Type::kStringSkS:
-            pun(fSkString)->~SkString();
+            fSkString.destroy();
             return;
         case Type::kObjRef:
         case Type::kObject:
@@ -59,7 +54,7 @@ SkPDFUnion SkPDFUnion::copy() const {
     switch (fType) {
         case Type::kNameSkS:
         case Type::kStringSkS:
-            new (pun(u.fSkString)) SkString(*pun(fSkString));
+            u.fSkString.init(fSkString.get());
             return u;
         case Type::kObjRef:
         case Type::kObject:
@@ -140,11 +135,10 @@ void SkPDFUnion::emitObject(SkWStream* stream,
             return;
         case Type::kNameSkS:
             stream->writeText("/");
-            write_name_escaped(stream, pun(fSkString)->c_str());
+            write_name_escaped(stream, fSkString.get().c_str());
             return;
         case Type::kStringSkS:
-            SkPDFUtils::WriteString(stream, pun(fSkString)->c_str(),
-                                    pun(fSkString)->size());
+            SkPDFUtils::WriteString(stream, fSkString.get().c_str(), fSkString.get().size());
             return;
         case Type::kObjRef:
             stream->writeDecAsText(objNumMap.getObjectNumber(fObject));
@@ -221,13 +215,13 @@ SkPDFUnion SkPDFUnion::String(const char* value) {
 
 SkPDFUnion SkPDFUnion::Name(const SkString& s) {
     SkPDFUnion u(Type::kNameSkS);
-    new (pun(u.fSkString)) SkString(s);
+    u.fSkString.init(s);
     return u;
 }
 
 SkPDFUnion SkPDFUnion::String(const SkString& s) {
     SkPDFUnion u(Type::kStringSkS);
-    new (pun(u.fSkString)) SkString(s);
+    u.fSkString.init(s);
     return u;
 }
 
diff --git a/src/pdf/SkPDFTypes.h b/src/pdf/SkPDFTypes.h
index c393376abb..10fe125aa6 100644
--- a/src/pdf/SkPDFTypes.h
+++ b/src/pdf/SkPDFTypes.h
@@ -5,10 +5,11 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkPDFTypes_DEFINED
 #define SkPDFTypes_DEFINED
 
+#include <type_traits>
+
 #include "SkRefCnt.h"
 #include "SkScalar.h"
 #include "SkTHash.h"
@@ -63,6 +64,20 @@ private:
 
 ////////////////////////////////////////////////////////////////////////////////
 
+template <class T>
+class SkStorageFor {
+public:
+    const T& get() const { return *reinterpret_cast<const T*>(&fStore); }
+    T& get() { return *reinterpret_cast<T*>(&fStore); }
+    // Up to caller to keep track of status.
+    template<class... Args> void init(Args&&... args) {
+        new (&this->get()) T(std::forward<Args>(args)...);
+    }
+    void destroy() { this->get().~T(); }
+private:
+    typename std::aligned_storage<sizeof(T), alignof(T)>::type fStore;
+};
+
 /**
    A SkPDFUnion is a non-virtualized implementation of the
    non-compound, non-specialized PDF Object types: Name, String,
@@ -129,7 +144,7 @@ private:
         bool fBoolValue;
         SkScalar fScalarValue;
         const char* fStaticString;
-        char fSkString[sizeof(SkString)];
+        SkStorageFor<SkString> fSkString;
         SkPDFObject* fObject;
     };
     enum class Type : char {