Contract Class

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Contains static methods for representing program contracts such as preconditions, postconditions, and object invariants.

Inheritance Hierarchy

System.Object
  System.Diagnostics.Contracts.Contract

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

Syntax

'Declaration
Public NotInheritable Class Contract

public static class Contract

The Contract type exposes the following members.

Methods

	Name	Description
	Assert(Boolean)	Checks for a condition; if the condition is false, follows the escalation policy set for the analyzer.
	Assert(Boolean, String)	Checks for a condition; if the condition is false, follows the escalation policy set by the analyzer and displays the specified message.
	Assume(Boolean)	Instructs code analysis tools to assume that the specified condition is true, even if it cannot be statically proven to always be true.
	Assume(Boolean, String)	Instructs code analysis tools to assume that a condition is true, even if it cannot be statically proven to always be true, and displays a message if the assumption fails.
	EndContractBlock	Marks the end of the contract section when a method's contracts contain only preconditions in the if-then-throw form.
	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.
	EnsuresOnThrow<TException>(Boolean)	Specifies a postcondition contract for the enclosing method or property, based on the provided exception and condition.
	EnsuresOnThrow<TException>(Boolean, String)	Specifies a postcondition contract and a message to display if the condition is false for the enclosing method or property, based on the provided exception and condition.
	Exists(Int32, Int32, Predicate<Int32>)	Determines whether a specified test is true for any integer within a range of integers.
	Exists<T>(IEnumerable<T>, Predicate<T>)	Determines whether an element within a collection of elements exists within a function.
	ForAll(Int32, Int32, Predicate<Int32>)	Determines whether a particular condition is valid for all integers in a specified range.
	ForAll<T>(IEnumerable<T>, Predicate<T>)	Determines whether all the elements in a collection exist within a function.
	Invariant(Boolean)	Specifies an invariant contract for the enclosing class.
	Invariant(Boolean, String)	Specifies an invariant contract for the enclosing class, and displays a message if the condition for the contract fails.
	OldValue<T>	Represents values as they were at the start of a method or property.
	Requires(Boolean)	Specifies a precondition contract for the enclosing method or property.
	Requires(Boolean, String)	Specifies a precondition contract for the enclosing method or property, and displays a message if the condition for the contract fails.
	Requires<TException>(Boolean)	Specifies a precondition contract for the enclosing method or property, and throws an exception if the condition for the contract fails.
	Requires<TException>(Boolean, String)	Specifies a precondition contract for the enclosing method or property, and throws an exception with the provided message if the condition for the contract fails.
	Result<T>	Represents the return value of a method or property.
	ValueAtReturn<T>	Represents the final (output) value of an out parameter when returning from a method.

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Remarks

Code contract classes let you specify preconditions, postconditions, and object invariants in your code. Preconditions are requirements that must be met when entering a method or property. Postconditions describe expectations at the time the method or property code exits. Object invariants describe the expected state for a class that has no condition problems. For more information about preconditions, postconditions, and object invariants, see Code Contracts.

For tools and detailed instructions for using code contracts, see Code Contracts on the MSDN DevLabs Web site.

Important Note:

You must use a binary rewriter to insert run-time enforcement of contracts. Otherwise, contracts such as the Contract.Ensures method can only be tested statically and will not throw exceptions during run time if a contract is violated. You can download the binary rewriter CCRewrite from Code Contracts on the MSDN DevLabs Web site. CCRewrite comes with a Visual Studio add-in that enables you to activate run-time contract enforcement from the project Properties page. The binary rewriter and the Visual Studio add-in do not ship with Visual Studio 2010 or the Windows SDK.

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.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

See Also

Reference

System.Diagnostics.Contracts Namespace