Liskov Substitution Principle

LSP

Kind: principle

Layer: Structural Core

Aliases: LSP, Liskov Substitution Principle, Behavioral Subtyping

Record: architecture:liskov-substitution

Severity: mandatory

Scope: class, interface, type hierarchy

Canonical: Ontology

A design rule that a subtype can replace its base type anywhere, because it keeps the base type's preconditions, postconditions and invariants.

Listed in Architecture principles, after Open/Closed Principle (OCP) and before Polymorphism.

Requires

• Contract Preservation
• Preconditions
• Postconditions
• Invariant

Reinforces

• Polymorphism
• Type Safety

Enables

• Safe Substitution
• Substitutability

Conflicts with

• Broken Inheritance
• Broken Inheritance

In tension with

• Narrow Specialized Behavior

Tensions

• Liskov Substitution Principle (LSP) / Narrow Specialized Behavior

Violated by

• Broken Inheritance

Refactored by

• Replace Inheritance with Delegation
• Extract Interface
• Split Hierarchy

Severity

• mandatory

Category

• SOLID / Object-Oriented Design

Enabled by

• Design by Contract

Linked from

• The structural domain
• Contracts / Interfaces / Compatibility
• SOLID / Object-Oriented Design
• Schema / Canonical Data / Semantics
• Core Vocabulary
• Quality Attributes
• SOLID / Object-Oriented Design
• Severity levels
• The resolutions