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Experiment - "Proper" properties

 
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Brent
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Joined: 01 Jul 2005
Posts: 728

PostPosted: Sep 5th, 2014, 9:29pm    Post subject: Experiment - "Proper" properties Reply with quote

I was recently re-examining VF's property syntax and decided it was a bit flawed. I haven't been entirely happy with the implicit property approach, so I think I'll be giving VF "proper" properties.

Here's an example of the syntax I have in mind in its simplest form. It strongly resembles a Dim/Var declaration.
Code:
Class Pen
  Property Color As UInt
End Class

Pen #pen
#pen Color = &HFF0000
End

You can associate getter and setter methods with a property by using the ON keyword.
Code:
Property name
  [ On Get
    [statements] ]
  [ On Set param
    [statements] ]
End Property


Let's say we want to prevent invalid values being assigned to Color.
Code:
Class Pen
   Property Color As UInt
     On Set value
       value And= &HFFFFFF
   End Property
End Class

If you are familiar with VB.NET, the following is functionally equivalent to the above code.
Code:
Public Class Pen
  Private _color As Integer
  Public Property Color() As Integer
    Get
      Return _color
    End Get
    Set (ByBal value As Integer)
      _color = value And &HFFFFFF
    End Set
  End Property
End Class

Here are some things to notice:
  • VF's properties will allocate a variable for you.
  • VF's properties are always public.
  • VF's use of "Get" and "Set" do not represent keywords. They are simply labels that can be anything you want.
  • VF's setter method assumes its parameter has the same type as the property itself.
  • VF's getter and setter are simply guard clauses. They do not explicitly return or modify the underlying variable, but instead can prevent or override the default behavior.

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Brent
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STPendl
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Joined: 20 Aug 2007
Posts: 161
Location: Austria

PostPosted: Sep 7th, 2014, 11:37am    Post subject: Re: Experiment - "Proper" properties Reply with quote

I like your approach, which contains some helpful automatisms.

Having to specify the type of the parameters twice is really something that should be avoided.
.NET is good, but it has its own syntactical drawbacks.

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Stefan

Any code I post can be freely used, just give credit.
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