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4993 :: can already defined types be modified at compile time with a macro?

• JohnAD (orginal) [2019-07-07T06:54:04+02:00] view original

  I can write a macro that allows me to do this:

  my_macro_adds_age:
    type
      SomeType = object
        name: string
  
  let a = SomeType(name: "Bob", age: 30)
  Run

  No problem.

  But, I'm curious, is it even possible (and safe) to modify a type after the definition? Something akin to:

  type
    SomeType = object
      name: string
  
  my_other_macro_adds_age(SomeType)
  
  let a = SomeType(name: "Bob", age: 30)
  Run

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• leorize (orginal) [2019-07-07T07:14:37+02:00] view original

  Macros can only create ASTs, they can't modify them. It'd be really dangerous if it could, since you wouldn't know where the macro executes.

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