Mirror of forum.nim-lang.org

4528 :: Creating instance of ptr "object" from instance of "object"

• calebwin (orginal) [2019-01-03T21:28:01+01:00] view original

  So I'm trying to embed Python in Nim using the nim-lang/python port.

  In src/python.nim there's this code -

  
  PyMethodDefPtr* = ptr PyMethodDef
  PyMethodDef*{.final.} = object  # structmember.h
    mlName*: cstring
    mlMeth*: PyCFunction
    mlFlags*: int
    mlDoc*: cstring
  Run

  I know how to create an instance of PyMethodDef -

  
  let myMethodDef: PyMethodDef = PyMethodDef(mlName : "myMethodName", mlMeth : myMethod)
  Run

  where myMethod is of type PyCFunction that is defined as a specific proc signature.

  But I don't know how to create an instance of PyMethodDefPtr to pass into some other function. Can someone help me out?

---

• Stefan_Salewski (orginal) [2019-01-03T22:09:33+01:00] view original

  I may miss something...

  You know alloc and alloc0 from manual? That procs can be use to allocate memory for untraced pointers on the heap. Like

  
  var myMethodDef: PyMethodDefPtr = cast[PyMethodDefPtr](alloc0(sizeof(PyMethodDef))
  myMethodDef[] = PyMethodDef(mlName : "myMethodName", mlMeth : myMethod)
  Run

  First line allocates memory, second line copies data. Of course untested, I think I have never used alloc() myself yet.

---

• leorize (orginal) [2019-01-15T04:55:41+01:00] view original

  You should use create() (docs) instead:

  var myMethodDef: PyMethodDefPtr = create(PyMethodDef)
  Run

---

• leorize (orginal) [2019-01-15T04:57:17+01:00] view original

  You might be interested in nimpy

---

• Araq (orginal) [2019-01-15T09:18:19+01:00] view original

  Use addr or unsafeAddr to turn it into a ptr. There shouldn't be a need to allocate this on the heap via alloc.

---