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Contract.OldValue(Of T) Method

Represents values as they were at the start of a method or property.

Namespace:  System.Diagnostics.Contracts
Assembly:  mscorlib (in mscorlib.dll)

Public Shared Function OldValue(Of T) ( _
	value As T _
) As T

Type Parameters


The type of value.


Type: T
The value to represent (field or parameter).

Return Value

Type: T
The value of the parameter or field at the start of a method or property.

This method can be used only in the conditional expression for the Ensures contract.

The following example shows the use of the OldValue(Of T) method to ensure that a count has been updated. This code example is part of a larger example provided for the ContractClassAttribute class.

Sub Insert(ByVal index As Integer, ByVal value As [Object]) Implements IArray.Insert
    Contract.Requires(index >= 0)
    Contract.Requires(index <= CType(Me, IArray).Count) ' For inserting immediately after the end.
    Contract.Ensures(CType(Me, IArray).Count = Contract.OldValue(CType(Me, IArray).Count) + 1)

End Sub 'IArray.Insert

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.