Add pattern matchers for SkRecord

src/utils/SkTLogic.h

Index: src/utils/SkTLogic.h
diff --git a/src/utils/SkTLogic.h b/src/utils/SkTLogic.h
index 62952ad13c267d88e911a34a25a34cebc2bd5835..c97849d2da2be5408216a917c0da153be24f6633 100644
--- a/src/utils/SkTLogic.h
+++ b/src/utils/SkTLogic.h
@@ -89,4 +89,11 @@ public:
     static const bool value = sizeof(func<Derived>(NULL)) == sizeof(uint16_t);      \
 }
 
+/** SK_WHEN_TYPE is type T if cond_type exists, otherwise it does not exist.
+ *  You can use this to enable specializations conditioned on whether a type exists.
+ */
+#define SK_WHEN_TYPE(cond_type, T) typename SkWhenType<cond_type, T>::type
+template <typename cond_type, typename T>
+struct SkWhenType { typedef T type; };
+

[bungeman-skia, 2014/05/05 19:37:51]

So it seems the 'normal' way to do this would be to have a member type trait
detector like

#define SK_CREATE_TYPEDEF_DETECTOR(type) \
template <typename T> \
class HasTypedef_##type { \
    template <typename C> static uint8_t func(typename C::foobar*); \
    template <typename> static uint16_t func(...); \
public: \
    static const bool value = sizeof(func<T>(NULL)) == sizeof(uint8_t); \
}

and then

SK_CREATE_TYPEDEF_DETECTOR(type);
SK_WHEN(HasTypedef_type<MyType>, void)

Of course, this is also more complex and less flexible. It is more complex in
that it converts the existence to a bool and then picks T or nothing based on
the bool, as opposed to directly picking T or nothing based on the existence of
the type directly. It also introduces the extra HasTypedef_type name. It does
not handle top level typedefs (though I'm not sure one would want to do that,
maybe that limitation is a feature). On the other hand, it's more uniform to
current usage and removes the SkWhenType and SK_WHEN_TYPE names.

[mtklein, 2014/05/05 20:05:12]

Strongly agreed and done.

 #endif