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885 :: Doc for Marshal

• Wink (orginal) [2015-02-17T18:18:39+01:00] view original

  Just discovered nim I'm interested in IPC so looked at Marshal and tired to compile a tidbit there:

  type
    TA = object
    TB = object of TA
      f: int
  
  var
    a: ref TA
    b: ref TB
  
  new(b)
  a = b
  echo($$a[]) # produces "{}", not "{f: 0}"
  Run

  I tired to compile it with 10.2 and got the following error:

  
  wink-macbookpro2:x wink$ nim c -r y.nim
  config/nim.cfg(45, 2) Hint: added path: '/Users/wink/.babel/pkgs/' [Path]
  config/nim.cfg(46, 2) Hint: added path: '/Users/wink/.nimble/pkgs/nimble-0.6.0' [Path]
  config/nim.cfg(46, 2) Hint: added path: '/Users/wink/.nimble/pkgs/' [Path]
  Hint: used config file '/Users/wink/foss/nim/config/nim.cfg' [Conf]
  Hint: system [Processing]
  Hint: y [Processing]
  y.nim(3, 14) Error: inheritance only works with non-final objects
  Run

  So searched the net and apparently TA needs to be "inheritable":

  type
    TA {.inheritable.} = object
  Run

  I recompiled then got a second error:

  
  y.nim(12, 5) Error: undeclared identifier: '$$'
  Run

  So I replaced '$$a[]' with '$a[]' in the echo statement and it worked:

  
  /Users/wink/prgs/nim-pg/x/y
  ()
  Run

  The "final" code is:

  wink-macbookpro2:x wink$ cat y.nim
  type
    TA {.inheritable.} = object
    TB = object of TA
      f: int
  
  var
    a: ref TA
    b: ref TB
  
  new(b)
  a = b
  echo($a[]) # produces "{}", not "{f: 0}"
  Run

  If my solution is "correct" I'd be happy to provide a patch to the documentation of lib/pure/marshal.nim.

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• Jehan (orginal) [2015-02-17T18:28:20+01:00] view original

  You need to import marshal for $$ to work. $ is the string operator.

  import marshal
  
  type
    TA {.inheritable.} = object
    TB = object of TA
      f: int
  
  var
    a: ref TA
    b: ref TB
  
  new(b)
  a = b
  
  echo($$a)
  echo($$b)
  Run

  That said, $$ does not seem to work correctly with inheritance regardless.

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• Wink (orginal) [2015-02-17T19:08:05+01:00] view original

  So I tried this:

  import marshal
  
  type
    Person {.inheritable.} = object
      age: int
      name: string
    Job = object of Person
      title: string
  
  
  var p = Person(age: 38, name: "Torbjørn")
  var j: Job
  j.age = p.age
  j.name = p.name
  j.title = "Programmer"
  
  echo($$p)
  echo($$j)
  Run

  And the output is below, is this correct?

  
  {"age": 38, "name": "Torbj\u00F8rn"}
  {"title": "Programmer", "age": 38, "name": "Torbj\u00F8rn"}
  Run

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• Jehan (orginal) [2015-02-17T19:14:35+01:00] view original

  Wink: And the output is below, is this correct?

  That would seem to be correct. Note that while the serialized form does not include type information, that's derived during the unmarshaling process from the declared type of the result.

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