Invariant Contract

• Aug 03, 2020
• 2 minutes to read

Purpose

This Code Provider adds the Invariant precondition to method parameter(s) or a variable assignment. The precondition ensures the passed or returned parameters are not empty throughout the method’s life-cycle.

Availability

Available in the following cases.

• When the caret is at the beginning of a method body. In this case, the contract will test all method parameters and strings.
• When the caret is on a method’s parameter name. In this case, the contract will test only the selected parameter.
• When the caret is on a variable assignment.

Note

This Code Provider may be unavailable for variables of a non-nullable type, for instance, Integer.

Usage

1. Place the caret at the beginning of a method body.

   Note

   The blinking cursor shows the caret’s position at which the Code Provider is available.

   C#

   public void AddRecord(string name, object data) {│
   //...
   }
   

   VB.NET

   Public Sub AddRecord(ByVal name As String, ByVal data As Object)│
   '...
   End Sub
   

2. Press the Ctrl + . or Ctrl + ~ shortcut to invoke the Code Actions menu.
3. Select Add Contract | Contract.Invariant Contract from the menu.

After execution, the Code Provider adds the assumption statement against all the method parameters.

C#

public void AddRecord(string name, object data) {
    Contract.Invariant(!string.IsNullOrEmpty(name), "name is null or empty.");
    Contract.Invariant(data != null, "data is null.");

    //...
}

VB.NET

Public Sub AddRecord(ByVal name As String, ByVal data As Object)
    Contract.Invariant(Not String.IsNullOrEmpty(name), "name is nothing or empty.")
    Contract.Invariant(data IsNot Nothing, "data is nothing.")

    '...
End Sub

You can ask CodeRush to check arrays and collections length in code contracts. Refer to the Code Actions Settings topic for more information.

Note

If the source file does not contain reference to the System.Diagnostics.Contracts namespace, CodeRush adds the corresponding reference.