Backreferences?

[bfoz]

What's the Qo-ish way to affect something similar to backreferences?

For example, match a Hash where the value of the :foo key matches the value of the :bar key.

# This doesn't work
Qo[:foo => :bar, :bar => :foo] === {foo:42, bar:42}    # => false

[baweaver]

It'd try and do literal compare -> methodized compare. Back references don't currently work as Qo has no idea of that level of introspection.

[baweaver]

Now as to how to do that, it'd have to be an entirely different syntax.

I could see something along the lines of adding a handler to Qo:

Qo2 = Qo.with(back_reference: true, bidirectional_matching: true)

Qo2[:foo => :bar, :bar => :foo] === {foo:42, bar:42} # true

[bfoz]

How about something like...

Qo[foo: Qo[:bar], bar: Q[:foo]]

That would requiring modifying the hash matcher to notice that the value matcher is another Qo, and then apply it to the target object to get the value to be matched. It would be a small performance penalty, which I know you're against, but it makes the syntax cleaner.

[bfoz]

As soon as I posted that I thought of an another idea. Funny how that works.

Taking a page from the Any concept: make an explicit backreference matcher object. Call it BR, for lack of a better idea.

Qo[foo: BR[:bar], bar: BR[:foo]]

[baweaver]

Thinking about this in the process of releasing 0.99, this seems a bit out of place for the current API.