Propertyproperty

Declares or defines a property in a type or class

Syntax

{ Type | Class } typename

Declare Property fieldname () [ ByRef ] As datatype

Declare Property fieldname ( [ ByRef | ByVal ] new_value As datatype )

Declare Property fieldname ( [ ByRef | ByVal ] index As datatype ) [ ByRef ] As datatype

Declare Property fieldname ( [ ByRef | ByVal ] index As datatype, [ ByRef | ByVal ] new_value As datatype )

End { Type | Class }

Property typename.fieldname () [ ByRef ] As datatype [ Export ]

statements

Parameters

Name		Description
`typename`		name of the `Type` or `Class`
`fieldname`		name of the property
`new_value`		the value passed to property to be assigned
`index`		the property index value

Description

Property fields are used to get and set values of a Type or Class in the same way as other data fields except instead of a simple assignment to a field or a value retrieved from field, a procedure is executed.

typename is the name of the type for which the Property method is declared and defined. Name resolution for typename follows the same rules as procedures when used in a Namespace.

A Property may optionally have one index parameter. When indexed, properties are accessed as fieldname(Index) [ = value ].
A Property without index parameter must always be used without empty parentheses after fieldname.
A get-Property can also return a reference by specifying ByRef As return_type.

A hidden This parameter having the same type as typename is passed to the property procedure. This is used to access the fields of the Type or Class.

Note: A standard Property (get & set) does not work with combination operators (as "+="). But a result byref get-Property (as more generally any result byref function) works with combination operators.

Note: When a get-Property is defined with one index parameter, the fieldname= syntax can not be used to return a value. For such a get-Property, the property= syntax (in addition to the Return syntax) is only the one allowed.

Remarks

Example

Type Vector2D

  As Single x, y

  Declare Operator Cast() As String

  Declare Property Length() As Single

  Declare Property Length( ByVal new_length As Single )

End Type



Operator Vector2D.cast () As String

  Return "(" + Str(x) + ", " + Str(y) + ")"

End Operator



Property Vector2D.Length() As Single

  Length = Sqr( x * x + y * y )

End Property



Property Vector2D.Length( ByVal new_length As Single )

  Dim m As Single = Length

  If m <> 0 Then

    '' new vector = old / length * new_length

    x *= new_length / m

    y *= new_length / m

  End If

End Property



Dim a As Vector2D = ( 3, 4 )



Print "a = "; a

Print "a.length = "; a.length

Print



a.length = 10



Print "a = "; a

Print "a.length = "; a.length

Output:

a = (3, 4)
a.length =  5

a = (6, 8)
a.length =  10

Property Indexing:

'' True/False

Namespace BOOL

  Const False = 0

  Const True = Not False

End Namespace



Type BitNum

  Num As UInteger

  

    '' Get/Set Properties each with an Index.

  Declare Property NumBit( ByVal Index As Integer ) As Integer

  Declare Property NumBit( ByVal Index As Integer, ByVal Value As Byte )

End Type



  '' Get a bit by it's index.

Property BitNum.NumBit( ByVal Index As Integer ) As Integer

  Return Bit( This.Num, Index )

End Property



  '' Set a bit by it's index.

Property BitNum.NumBit( ByVal Index As Integer, ByVal Value As Byte )



    '' Make sure index is in Integer range.

  If Index >= ( SizeOf(This.Num) * 8 ) Then

    Print "Out of uInteger Range!"

    Exit Property

  Else

    If Index < 0 Then Exit Property

  End If

  

  If Value = BOOL.FALSE Then

    This.Num = BitReset( This.Num, Index )

  End If

  

  If Value = BOOL.TRUE Then

    This.Num = BitSet( This.Num, Index )

  End If

  

End Property





Dim As BitNum Foo





Print "Testing property indexing with data types:"

Print "FOO Number's Value: " & Foo.Num



  '' Set the bit in the number as true.

Foo.NumBit(31) = BOOL.TRUE

Print "Set the 31st bit of FOO"



  '' Print to see if our bit has been changed.

Print "FOO Number's Value: " & Foo.Num

Print "FOO 31st Bit Set? " & Foo.NumBit(31)

Sleep

Print ""