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3576 :: properties fo objects

• r3d9u11 (orginal) [2018-02-24T09:09:31+01:00] view original

  Hi, I need a help with properties. Why setter isn't call? Also how to set property "title" to readonly state (disable setter)?

  type
    Info* = ref object of RootObj
      level: int
      title: string
  
  proc `level=`*(info: var Info, level: int) {.inline.} =
    info.level = level
    info.title = "Level " & $(level)
  
  var info: Info
  new info
  
  info.level = 5
  
  echo info.title
  Run

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• def (orginal) [2018-02-24T09:27:38+01:00] view original

  In the same module you can do: info.`level=`(5)

  From another module, if the level field is private, you can just do info.level = 5.

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• Stefan_Salewski (orginal) [2018-02-24T09:41:01+01:00] view original

  r3d, the source of your problem is obviously that your setter proc has exactly the same name as a member field.

  def, maybe you should add your above info to manual.

  I had the feeling that this variant would work:

  type
    Info* = ref object of RootObj
      level: string
      title: string
  
  proc `level=`*(info: var Info, level: int) =
    info.level = $level
    info.title = "Level " & $(level)
  
  var info: Info
  new info
  
  info.level = 5
  
  echo info.title
  Run

  But still setter proc has no priority:

  
  h.nim(13, 12) Error: type mismatch: got (int literal(5)) but expected 'string'
  Run

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• r3d9u11 (orginal) [2018-02-24T10:10:00+01:00] view original

  The manual page shows that setter have same name as field of object. And it is implicitly called (s.host = 34). What differents?

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• Stefan_Salewski (orginal) [2018-02-24T10:19:13+01:00] view original

  r3d9, in manual field name is plain h, proc name is host.

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• r3d9u11 (orginal) [2018-02-24T10:21:13+01:00] view original

  Yep, but host and h are both fields of Socket, no? (Perhaps I do not fully understand procedural programming for the present, I'm used to OOP only defore). Ok, it is works: main.nim:

  import InfoModule
  
  var info: Info
  new info
  
  info.level = 5
  # info.title = "smth title..." # error, because read only access
  
  echo info.title
  Run

  InfoModule.nim

  type
    Info* = ref object of RootObj
      level: int
      title: string
  
  proc `level=`*(info: var Info, value: int) {.inline.} =
    info.level = value
    info.title = "Level " & $(value)
  
  proc `title`*(info: var Info): string {.inline.} =
    info.title
  Run

  I think, that would be cool if behavior of properties will be more detailed examined in manual. Especially differents behavior inside and outside of the source module :) Thank you all for your help!

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• Stefan_Salewski (orginal) [2018-02-24T10:34:41+01:00] view original

  Yep, but host and h are both fields of Socket, no?

  No. In example in manual Socket datatype has only field h. Getter and setter procs host() and host= are ordinary procs which do access field h. The proc name notation "host=" is only syntactic sugar for making using it easier, as it looks like plain assignment.

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• mratsim (orginal) [2018-02-25T13:42:37+01:00] view original

  The manual suggest adding the F (field) prefix for properties to use with getter/setter: https://nim-lang.org/docs/manual.html#procedures-properties

  type
    Info* = ref object of RootObj
      Flevel: int
      Ftitle: string
  
  proc `level=`*(info: var Info, level: int) {.inline.} =
    info.Flevel = level
    info.Ftitle = "Level " & $(level)
  
  var info: Info
  new info
  
  info.level = 5
  
  echo info.Ftitle
  
  Run

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