crystal class 宏未编译

Question

为了

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

我得到了

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

为什么？并将 @a 设置为 nil 确实解决了问题，但我认为这不是一个好的解决方法。

这是错误、设计限制还是我没有做正确的事？

Answer 1

是的，目前这是一个设计限制。引用来自 https://github.com/crystal-lang/crystal/issues/2731

的 Ary

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 宏未编译

crystal class with macro not compiling

crystal-lang