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Contract.OldValue<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 static T OldValue<T>(
	T value
)

Type Parameters

T

The type of 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.

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);
}

.NET Framework

Supported in: 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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