Contract.OldValue(T) Contract.OldValue(T) Contract.OldValue(T) Contract.OldValue(T) Method


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

generic <typename T>
 static T OldValue(T value);
public static T OldValue<T> (T value);
static member OldValue : 'T -> 'T
Public Shared Function OldValue(Of T) (value As T) As T
Type Parameters

The type of value.


The value to represent (field or parameter).


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


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

void IArray.Insert(int index, Object value)
    Contract.Requires(index >= 0);
    Contract.Requires(index <= ((IArray)this).Count);  // For inserting immediately after the end.
    Contract.Ensures(((IArray)this).Count == Contract.OldValue(((IArray)this).Count) + 1);
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


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

Applies to