Contract.Ensures Method

Definition

Namespace:

System.Diagnostics.Contracts

Assemblies:

netstandard.dll, System.Diagnostics.Contracts.dll

Specifies a postcondition contract for the enclosing method or property.

Overloads

Ensures(Boolean)	Specifies a postcondition contract for the enclosing method or property.
Ensures(Boolean, String)	Specifies a postcondition contract for a provided exit condition and a message to display if the condition is false.

Ensures(Boolean)

Source:

Contracts.cs

Specifies a postcondition contract for the enclosing method or property.

C#

[System.Diagnostics.Conditional("CONTRACTS_FULL")]
public static void Ensures(bool condition);

Parameters

condition

Boolean

The conditional expression to test. The expression may include OldValue<T>(T), ValueAtReturn<T>(T), and Result<T>() values.

Attributes

ConditionalAttribute

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.

C#

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);
}

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 Visual Studio Marketplace) for run-time enforcement of this postcondition.

Ensures(Boolean, String)

Source:

Contracts.cs

Specifies a postcondition contract for a provided exit condition and a message to display if the condition is false.

C#

[System.Diagnostics.Conditional("CONTRACTS_FULL")]
public static void Ensures(bool condition, string? userMessage);

Parameters

condition

Boolean

The conditional expression to test. The expression may include OldValue<T>(T) and Result<T>() values.

userMessage

String

The message to display if the expression is not true.

Attributes

ConditionalAttribute

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.

• This contract is exposed to clients; therefore, it must only reference members that are at least as visible as the enclosing method.

• You must use the binary rewriter (available at Code Contracts on the Visual Studio Marketplace) for run-time enforcement of this postcondition.

• If userMessage is not a constant string literal, the contract may not be understood by tools.