Article
11/18/2011

Contract.Ensures Method (Boolean)

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Specifies a postcondition contract for the enclosing method or property.

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

Syntax

'Declaration
<ConditionalAttribute("CONTRACTS_FULL")> _
Public Shared Sub Ensures ( _
    condition As Boolean _
)

[ConditionalAttribute("CONTRACTS_FULL")]
public static void Ensures(
    bool condition
)

Parameters

condition
Type: System.Boolean
The conditional expression to test. The expression may include OldValue<T>, ValueAtReturn<T>, and Result<T> values.

Remarks

The condition parameter specifies a postcondition that is expected to be true when the enclosing method or property returns normally.

This method call must be at the beginning of a method or property, before any other code.
You must use the binary rewriter (available at Code Contracts on the MSDN DevLabs Web site) for run-time enforcement of this postcondition.

Examples

The following example shows how to use the Ensures method to ensure that an expected value is returned. This code example is part of a larger example provided for the ContractClassAttribute class.

Function Add(ByVal value As Object) As Integer Implements IArray.Add
    ' Returns the index in which an item was inserted.
    Contract.Ensures(Contract.Result(Of Integer)() >= -1) '
    Contract.Ensures(Contract.Result(Of Integer)() < CType(Me, IArray).Count) '
    Return 0

End Function 'IArray.Add

int IArray.Add(Object value)
{
    // Returns the index in which an item was inserted.
    Contract.Ensures(Contract.Result<int>() >= -1);
    Contract.Ensures(Contract.Result<int>() < ((IArray)this).Count);
    return default(int);
}

Version Information

Silverlight

Supported in: 5, 4

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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