Type parameter is not correctly inferred for private inner class?

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1 
class Parent(T)
  private class Node(T)
    @child : Node(T) | Nil

    property :child

    def initialize(@child)
    end
  end

  def initialize
    node = Node(T).new(nil)
    node.child = node
  end
end

Parent(Int32).new

With crystal 1.7.2, this results in compilation error.

$ crystal build temp.cr
Showing last frame. Use --error-trace for full trace.

In temp.cr:13:18

 13 | node.child = node
                   ^---
Error: expected argument #1 to 'Parent::Node(Int32)#child=' to be ::Nil | Parent::Node(T), not Parent::Node(Int32)

Overloads are:
 - Parent::Node(T)#child=(child : ::Nil | Parent::Node(T))

If I remove private from Node class, the compilation succeeds.

Is this a bug, or documented behavior?

2

It also seems to work if you do property child : Node(T) | Nil instead of:

@child : Node(T) | Nil

property :child

So i’d say that’s unexpected? Maybe it’s messing up the type so the compiler thinks node isn’t actually Node(T) or something along those lines.

3

Yeah, this very much looks like unintended behaviour, i.e. a bug.
Could you report it in the issue tracker, please? https://github.com/crystal-lang/crystal/issues/new