Design by Contract

Kind: principle

Layer: Contracts Core

Aliases: DbC

Record: architecture:design-by-contract

Severity: recommended

Scope: API, function, class, service

Canonical: Ontology

A design rule that every operation states the preconditions it needs, the postconditions it guarantees and the invariants it keeps.

Listed in Architecture principles, after PACELC Theorem and before Explicit Contracts.

Requires

• Preconditions
• Postconditions
• Invariant

Reinforces

• Correctness
• Predictability

Enables

• Contract Testing
• Liskov Substitution Principle (LSP)

Conflicts with

• Implicit Behavior

In tension with

• Development Speed

Tensions

• Design by Contract / Development Speed

Contracts

• Architectural Contract Algebra
• Contract-Based Verification Kernel

Violated by

• Implicit Assumptions
• Trusting Invalid Inputs

Refactored by

• Precondition Check
• Postcondition Check
• Invariant Check

Severity

• recommended

Category

• Contracts / Interfaces / Compatibility

Linked from

• Template families
• A seat is a contract
• Stating an invariant
• From intent to predicate
• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• SOLID / Object-Oriented Design
• Error Handling / Resilience
• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• Error Handling / Resilience
• Architecture
• Context verification
• Severity levels
• The resolutions