Metalama Contracts facilitate the implementation of Contract-Based Programming principles, a software engineering practice that significantly enhances software reliability and clarity. In contract-based programming, a contract defines a set of obligations and expectations between two parties: a caller and a callee. Metalama Contracts embody three fundamental concepts of contract-based programming: preconditions, postconditions, and type invariants.
Preconditions ensure that necessary conditions are met before a method executes, while postconditions verify the results after execution. This enforcement aids in early error detection, preventing a defect in one component from manifesting in another. For example, when preconditions are properly enforced, a NullReferenceException in a component can be attributed to the component itself, whereas an ArgumentException thrown by a method shifts the blame to its caller. Similarly, Metalama Contracts introduce a new exception type, PostconditionViolationException, indicating that the method throwing it is responsible for the defect.
Type invariants are conditions that remain true throughout the entire lifetime of an instance of a type. Type invariants are useful in diagnosing defects in types with mutable states and complex logic.
Adhering to these contracts promotes modular and decoupled design, fostering system extensibility and adaptability. Overall, enforcing preconditions and postconditions is a pragmatic practice crucial for creating maintainable, reliable, and scalable software systems.
Compared to hand-written precondition checks, Metalama Contracts offer the following benefits:
More readable: Metalama Contracts are represented as custom attributes, resulting in less code to read and understand.
Inherited: You can add a Metalama contract attribute to an interface method parameter, and it's automatically enforced in all implementations of this method.
Customizable: It's easy to change the code generation pattern that throws the exception. For example, you can localize your exception messages as an afterthought, without any impact on your business code.
In this chapter
This chapter includes the following articles:
| Article | Description |
|---|---|
| Validating field, property, and parameter values | Describes how to add preconditions and postconditions to your fields, properties, and parameters. |
| Checking type invariants | Describes how to add type invariants and execute verification logic after the completion of all public methods. |
| Configuring contracts | Describes how to configure Metalama Contracts. |
| List of contract attributes | Lists all available contract attributes. |
| Checking all non-nullable fields, properties and parameters | Explains how to automatically enforce non-nullable declarations. |