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3469 :: Working with Objects

• drifter (orginal) [2018-01-09T18:46:35+01:00] view original

  Hi there,

  I'm working through the very excellent "Write an Interpreter in Go" (https://interpreterbook.com/)

  I'm trying to follow the book but implementing in nim rather than Go, but running into a wall trying to translate Go into Nim.

  For example passing pointers to objects or returning pointers to objects.

  An example in Go

  
  /* A lexer */
  type Lexer struct {
     input string
     position int
     readPosition int
     ch byte
  }
  
  /* Function to create a new lexer */
  func New(input string) *Lexer {
    l := &Lexer{input: input}
  }
  Run

  Translating to nim I have:

  type TLexer = object
    input     : string
    position  : int
    readPosition : int
    ch        : byte
  
  proc new(input : string) : TLexer =
    let l = new TLexer(input, 0, 0, 0)
    return l
  Run

  but I know I'm not doing this well. #1 Not sure how to create a Lexer object #2 Not sure how to return a pointer from a proc.

  Initially I tried defining the Lexer as

  type Lexer = ref object
   ...
  Run

  But that did not compile.

  I also tried defining the proc as

  proc New(input: string): ref Lexer =
   ....
  Run

  But also didn't compile.

  The nim way of working with objects is a bit new to me. I'm sure it's something very simple but not sure what is that little bit I'm nt getting.

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• woggioni (orginal) [2018-01-09T20:17:00+01:00] view original

  if you define Lexer as a reference type there is then no need to use the ref keyword anymore, your New function (in Nim the convention is to call it newLexer) would be simply

  proc newLexer(input: string): Lexer =
      ....
  Run

  and, under the hood, it would return a garbage collected pointer to an heap-allocated object

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• drifter (orginal) [2018-01-09T22:26:14+01:00] view original

  Thanks so much for this...pointer ;)

  Works like a charm now.

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