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1773 :: how to use typedesc in table?

• sunnyawake (orginal) [2015-11-07T02:27:35+01:00] view original

  i have some message types which all inherit super Message type,each Message has a code. i want to put all these messages type in a table and create type by code,something like this:

  var table=...
  table.add(1,LoginMessage)
  table.add(2,EnterGameMessage)
  ...
  
  proc createMessage(code:int):Message=
   new(table[code])

  how to new this table?

  tks

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• Araq (orginal) [2015-11-07T18:24:54+01:00] view original

  You cannot. 'typedesc' has no runtime representation and the RTTI doesn't support construction from type names. You can map an enum to your type hierarchy though and write a macro so that this mapping is not painful to maintain. This not unlike what other languages do under the hood to support these things.

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• yglukhov (orginal) [2015-11-07T18:30:20+01:00] view original

  @sunnyawake, take a look at: https://github.com/yglukhov/rod/blob/master/rod/component.nim specifically createComponent and registerComponent procs. They implement exactly your pattern.

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• sunnyawake (orginal) [2015-11-08T00:36:20+01:00] view original

  thanks for help,i've taken an easy way to do this:

  proc getMessage(code:int16):Message=
   case code
   of 1: CLogin(code:1)
   of 2: CSceneLoaded(code:2)
   ...

  all these code is generated from a xml message definition. i assume this method is O(1),am i right?

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