Mirror of forum.nim-lang.org

4689 :: Compile time type introspection

• Nycto (orginal) [2019-03-04T00:00:30+01:00] view original

  I'm trying to do some compile time type introspection, however I'm not getting the results I expect. Here is a minimal version of what I'm trying to do:

  # ---
  import macros
  
  type StructShape[T] = object
    fields: seq[tuple[key, typename: string]]
  
  macro getFields(struct: typedesc): seq[tuple[key, typename: string]] =
    echo "Type declartaion is: ", struct.getTypeImpl.repr
    @[]
  
  proc getShape*(struct: typedesc): StructShape[struct] =
    result.fields = getFields(struct)
  
  # ---
  
  type Foo = object
    bar: string
    baz: int
  
  let shape = getShape(Foo)
  Run

  I'm expecting the call to getTypeImpl to return the full AST of Foo's type declaration, but that isn't happening. Instead, I'm getting:

  
  Type declartaion is: typeDesc[Foo]
  Run

  I've tried this with 0.19.2 and 0.18.0

---

• Nycto (orginal) [2019-03-04T01:08:14+01:00] view original

  I did some deep diving and I've managed to answer my own question. This code gives me access to the type declaration:

  echo "Type declartaion is: ", struct.getTypeImpl[1].getTypeImpl.repr
  Run

  Though I couldn't tell you _why it needs to be like that.

---

• mratsim (orginal) [2019-03-04T10:52:15+01:00] view original

  You might want to use treerepr instead of repr

---