[SharedCache] Make MetadataSerializable::Load static

`MetadataSerializable` is updated to allow a subclass to optionally
specify the return type of `Load`. If not specified it defaults to the
subclass itself. `SharedCache` specifies `std::optional` to represent
the case where the serialized metadata is in a format or version it does
not recognize.

By making `Load` a static member function and having it return a new
object it becomes easier to reason about the state of objects when a
deserialization failure occurs. It can return `std::optional` to
indicate failure and there is no object left in an unknown state.

Prior to this, `Load` worked on an existing instance of an object. It
was unclear what state the object would be in if a deserialization
failure occurred (its original state prior to `Load`? some
partially-loaded state? a null state?). The failure itself also had to
be communicated out of band.

1 files changed, 3 insertions, 6 deletions

diff --git a/view/sharedcache/api/sharedcache.cpp b/view/sharedcache/api/sharedcache.cpp
index e764531c..472bb024 100644
--- a/view/sharedcache/api/sharedcache.cpp
+++ b/view/sharedcache/api/sharedcache.cpp
@@ -204,9 +204,8 @@ namespace SharedCacheAPI {
 		BNFreeString(outputStr);
 		if (output.empty())
 			return {};
-		SharedCacheMachOHeader header;
-		header.LoadFromString(output);
-		return header;
+
+		return SharedCacheMachOHeader::LoadFromString(output);
 	}
 
 	std::optional<SharedCacheMachOHeader> SharedCache::GetMachOHeaderForAddress(uint64_t address)
@@ -218,9 +217,7 @@ namespace SharedCacheAPI {
 		BNFreeString(outputStr);
 		if (output.empty())
 			return {};
-		SharedCacheMachOHeader header;
-		header.LoadFromString(output);
-		return header;
+		return SharedCacheMachOHeader::LoadFromString(output);
 	}
 
 	BNDSCViewState SharedCache::GetState()