OldValue(T) Method

Contract.OldValue<T> Method (T)

 

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

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

public static T OldValue<T>(
	T value
)

Parameters

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.

Type Parameters

T

The type of value.

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

The following example shows the use of the OldValue<T> 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);
}

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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