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2194 :: Identifier name as a variable

• stbalbach (orginal) [2016-04-09T21:20:01+02:00] view original

  Hello, first post and new to Nim.

  How would one use a variable in place of an identifier when referring to an object?

  Example:

  type
    LinksObj* = object
      origiaurl*: string
      formated*: string
      origurl*: string
  
  var Links = newSeq[LinksObj]()
  
  Links.insert(LinksObj(origiaurl: "none", formated: "none", origurl: "none"), 0)
  Links.insert(LinksObj(origiaurl: "some", formated: "some", origurl: "some"), 1)
  
  proc echoid(field: string): string =
    for link in Links:
      if link.origiaurl == "some":
        result = link.field
  
  echo echoid("formated")
  echo echoid("origurl")
  Run

  This produces a problem in 4th line from bottom

  • undeclared field: 'field'

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• bozaloshtsh (orginal) [2016-04-10T00:47:56+02:00] view original

  Not sure if it's possible but maybe the typeinfo module has what you need? It's what marshal uses to serialize arbitrary data types.

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• Araq (orginal) [2016-04-10T01:02:10+02:00] view original

  Use the system.fieldPairs iterator.

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• OderWat (orginal) [2016-04-10T01:13:04+02:00] view original

  I think OP could simply use a case / of construct if the strings are dynamic. If not he could probably use a macro instead but I don't really see the point in doing that. with the current code fragment. It would be easier to have "echoid_formated()" and "echoid_origurl()" or even just returning a ref to the object and accessing whats needed. Which is what you want to do if you don't want to have duplicate code for specialized versions anyway.

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• stbalbach (orginal) [2016-04-10T01:19:19+02:00] view original

  I came up with the following solution, but will look into fieldPairs as this method is cumbersome. This is indeed a code fragment IRL there are many more items in the object making separate procs for each unwieldy.

  type
    LinksObj* = object
      origiaurl*: string
      formated*: string
      origurl*: string
  
  var Links = newSeq[LinksObj]()
  
  Links.insert(LinksObj(origiaurl: "none", formated: "none", origurl: "none"), 0)
  Links.insert(LinksObj(origiaurl: "some", formated: "1234", origurl: "5678"), 1)
  
  proc fieldval(link: LinksObj, field: string): string {.discardable.} =
    if field == "origiaurl":
      return link.origiaurl
    elif field == "formated":
      return link.formated
    elif field == "origurl":
      return link.origurl
  
  proc echoid(field: string): string =
    for link in Links:
      if link.origiaurl == "some":
        result = fieldval(link, field)
  
  echo echoid("formated")
  echo echoid("origurl")
  Run

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• stbalbach (orginal) [2016-04-10T01:28:19+02:00] view original

  The new fieldval() with fieldPairs

  proc fieldval(link: LinksObj, field: string): string {.discardable.} =
    for name, value in link.fieldPairs:
      if name == field:
        return value
  Run

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