Derestricted_Operators.md

Derestricted Operators

Under the current rules of the VB.net language, some operators require to be implementation in complement pairs.

Op	Comp
<	=>
<=	>
>	<=
>=	<
<>	=
=	<>
IsTrue	IsFalse
IsFalse	IsTrue

Public Shared Operator <( x As Foo, y As Foo) As Boolean

End Sub

Public Shared Operator >=( x As Foo, y As Foo) As Boolean

End Sub

This proposal is to remove that restriction, by skip the following section of under a language feature conditional. Source

Or in proof of concept, commenting out the production of the error.

    diagnostics.Add(ErrorFactory.ErrorInfo(ERRID.ERR_MatchingOperatorExpected2,
      SyntaxFacts.GetText(OverloadResolution.GetOperatorTokenKind(nameOfThePair)),
      method), method.Locations(0))

---

Example

Module Module1

    Sub Main()
        Dim lower_limit = 0
        Dim upper_limit = 100
        Dim value_A = 50
        Dim value_B = -10
        Dim value_C = 180
        Dim res_A = lower_limit.__ < value_A <= upper_limit
        Dim res_B = lower_limit.__ < value_B <= upper_limit
        Dim res_C = lower_limit.__ < value_C <= upper_limit

    End Sub

End Module

Public Class CMPOP_A(Of T As IComparable(Of T))

    Private _Value As T

    Sub New(value As T)
        _Value = value
    End Sub

    ' First part of Range Check is done here. Also note we have to remember what the middle value is over to the next part.
    Public Shared Operator <(x As CMPOP_A(Of T), y As T) As CMPOP_B(Of T)   ' <-- Not a Boolean
        Return New CMPOP_B(Of T)(y, x._Value.CompareTo(y) < 0)
    End Operator

    Public Shared Operator <=(x As CMPOP_A(Of T), y As T) As CMPOP_B(Of T)   ' <-- Not a Boolean
        Return New CMPOP_B(Of T)(y, x._Value.CompareTo(y) <= 0)
    End Operator

End Class

Public Class CMPOP_B(Of T As IComparable(Of T))

    Private _Value As T
    Private _State As Boolean

    Sub New(Value As T, state As Boolean)
        _Value = Value
        _State = state
    End Sub

    ' If the State is False already it skips the comparison and returns False.
    Public Shared Operator <(x As CMPOP_B(Of T), y As T) As Boolean
        Return x._State AndAlso (x._Value.CompareTo(y) < 0)
    End Operator

    Public Shared Operator <=(x As CMPOP_B(Of T), y As T) As Boolean
        Return x._State AndAlso (x._Value.CompareTo(y) <= 0)
    End Operator

End Class

Public Module Exts
    <Runtime.CompilerServices.Extension>
    Public Function __(Of T As IComparable(Of T))(value As T) As CMPOP_A(Of T)
        Return New CMPOP_A(Of T)(value)
    End Function
End Module

When trying to use a now non-existent operator.

eg

Dim res_A = lower_limit.__ > value_A <= upper_limit

Error BC30452 Operator '>' is not defined for types 'CMPOP_A(Of Integer)' and 'Integer'.