Instantiate templated class at runtime
Aphex
Aphex at mail.com
Sun May 26 17:51:37 UTC 2019
I have been using Orange SerDes library for an application and
have run in to a major hurdle. I have the need to SerDes a
templated class. It seems Orange can only Serialize the class but
when it attempts to deserialize it at runtime it cannot build the
class.
It represents the type in the output as `Issue1.Y!string.Y` which
doesn't even seem right but regardless, it cannot seem to create
a new instance of Y!T.
I realize that the templates do not probably exist at runtime for
instantiation and so this is impossible, but Y!string surely does
exist since I create an object with it(although if separate paths
exist I could see how it could be an issue).
I need to be able to create such classes because it seems to be
the only limitation of deseralizing templates:
If, for example, I modify the instance creation code(in
Reflection.d):
Object newInstance (string name)
{
auto classInfo = ClassInfo.find(name);
if (!classInfo)
{
if (name == "Issue1.Y!string")
{
import Issue1;
return new Y!string;
}
if (name == "Issue1.Y!int")
{
import Issue1;
return new Y!int;
}
throw new Exception("Cannot find runtime class information for
`"~name~"` to instantiate!");
return null;
}
return newInstance(classInfo);
}
and manually create the classes then everything seems to work
great.
I have a few questions:
1. Is it possible to have a runtime class and struct creator
function that can deal with templates. It doesn't seem like it
should be that big a deal. One only needs to actually know the
size of class and that will depend on the template parameter
sizes, which if they are known then everything is known?
2. Is the output or Orange for templated classes correct?
"Issue1.Y!string.Y" or should it be "Issue1.Y!string"? Else this
is a bug that I'll need to track down and fix.
3. I figure that 1 might be a bit off so I will have to hack the
code to create a factory to build the various templated types
I'll use. This is not ideal.
In any case, my feeling is that ClassInfo should handle templated
classes too.
-------------- MWE ------------------------
import std.stdio;
import orange.serialization.Serializable : nonSerialized;
import std.file;
import orange.serialization._, orange.serialization.archives._;
class C
{
int x = 53;
}
class Y(T) : C
{
T x;
}
int main()
{
auto archive = new XmlArchive!(char); // create an XML archive
auto serializer = new Serializer(archive); // create the
serializer
serializer.register!(C);
serializer.register!(Y!int);
serializer.register!(Y!string);
C c = new C();
C[] ya;
auto yi = new Y!int;
yi.x = 22;
auto ys = new Y!string;
ys.x = "sfda";
ya ~= yi;
ya ~= ys;
auto slfp = `test.xml`;
if (!false && exists(slfp))
{
auto f = std.file.read(slfp);
archive.beginUnarchiving(cast(immutable(void)[])f);
auto ud = archive.untypedData;
ya = serializer.deserialize!(C[])(ud);
} else
{
// write xml file
archive.beginArchiving();
std.file.write(slfp, cast(byte[])serializer.serialize(ya));
}
return 0;
}
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