crystal class with macro not compiling

Question

for

class Y
  def initialize(@a : String)
  end
  getter a
end

class X
  macro test(name)
    @{{name}} = y.{{name}}
  end
  @a : String
  def initialize(y : Y)
    test a
  end
end

I got

instance variable '@a' of X was not initialized directly in all of the 'initialize' methods, rendering it nilable. Indirect initialization is not supported.

why? and set @a to nil did solve the problem but that's not a good workaround in my opinion.

Is it a bug, a design limit or just I'm not doing the right thing?

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

Yes, currently this is a design limitation. Quoting Ary from https://github.com/crystal-lang/crystal/issues/2731

Yes, this is expected behaviour. initialize must be simple enough for the compiler to analyze. A macro might be redefined in a subclass so resolving init is not trivial for a first pass.

This is a "won't fix" for me, or maybe we can mark it as an enhancement, but it won't happen soon (maybe never)

There's a hack I introduced to make initialization via macro possible: if {{@type}} is mentioned then the compiler will lazily check the method on call. It's not documented, though. And it has several bugs. But for now it might be okay.

crystal class with macro not compiling

1 Answers1