Question

OK, Ruby gurus, this is a hard one to describe in the title, so bear with me for this explanation:

I’m looking to pass a string that represents a variable: not an instance, not the collection of properties that make up an object, but the actual variable: the handle to the object.

The reason for this is that I am dealing with resources that can be located on the filesystem, on the network, or in-memory. I want to create URI handler that can handle each of these in a consistent manner, so I can have schemes like eg.

• file://
• http://
• ftp://
• inmemory://

you get the idea. It’s the last one that I’m trying to figure out: is there some way to get a string representation of a reference to an object in Ruby, and then use that string to create a new reference? I’m truly interested in marshalling the reference, not the object. Ideally there would be something like taking Object#object_id, which is easy enough to get, and using it to create a new variable elsewhere that refers to the same object. I’m aware that this could be really fragile and so is an unusual use case: it only works within one Ruby process for as long as there is an existing variable to keep the object from being garbage collected, but those are both true for the inmemory scheme I’m developing.

The only alternatives I can think of are:

• marshal the whole object and cram it into the URI, but that won’t work because the data in the object is an image buffer – very large
• Create a global or singleton purgatory area to store a variable for retrieval later using e.g. a hash of object_id:variable pairs. This is a bit smelly, but would work.

Any other thoughts, StackOverflowers?

Answer 1

There’s ObjectSpace._id2ref :

f = Foo.new #=> #<Foo:0x10036c9b8> 
f.object_id #=> 2149278940 
ObjectSpace._id2ref(2149278940) #=> #<Foo:0x10036c9b8>

In addition to the caveats about garbage collection ObjectSpace carries a large performance penalty in jruby (so much so that it’s disabled by default)