Liskov Substitution Principle (LSP)

Advanced Liskov Substitution Principle (LSP) in SOLID Design Principles Tutorial. Deep dive with production-oriented examples—not a shallow overview.

Architecture & mental model

This lesson covers Liskov Substitution Principle (LSP) at an intermediate-to-advanced level within SOLID Principles. You will connect C# concepts to production constraints: performance, security, testability, and operability.

Advanced learners should already know syntax basics; here we focus on why teams choose specific patterns and how they fail in real systems.

Implementation (production-style)

Type the code below; change names and types to match your domain. Compare with how C# teams structure layers in mature codebases.

// Liskov Substitution Principle (LSP) — SOLID Design Principles Tutorial
public sealed class LiskovSubstitutionPrinci
{
    private readonly ILogger _log;

    public LiskovSubstitutionPrinci(ILogger log)
        => _log = log;

    public async Task ExecuteAsync(CancellationToken ct = default)
    {
        _log.LogInformation("Applying concept: Liskov Substitution Principle (LSP)");
        await Task.CompletedTask;
    }
}

Decision checklist

• Requirements: What are latency, consistency, and security needs for "Liskov Substitution Principle (LSP)"?
• Boundaries: Which layer owns this logic (UI, API, domain, infrastructure)?
• Failure modes: What happens when dependencies time out or return partial data?
• Observability: What logs or metrics prove this feature works in production?

Hands-on lab (45–60 min)

1. Reproduce the primary example for "Liskov Substitution Principle (LSP)" in a scratch project using C#.
2. Add one automated test (unit or integration) that would fail if you break the core behavior.
3. Introduce a deliberate bug (wrong lifetime, missing await, wrong dependency order) and observe the symptom.
4. Document one trade-off you would present in a design review.

Pitfalls senior engineers avoid

• Treating tutorial demos as production architecture without hardening.
• Skipping observability (logs, metrics, traces) when adding complexity.
• Optimizing before measuring bottlenecks.
• Ignoring team conventions and existing codebase patterns.

Interview depth

Question: Explain Liskov Substitution Principle (LSP) to a junior developer in 2 minutes, then list two trade-offs.

Strong answer: Start with the problem it solves, describe one real project usage, mention a failure you debugged or would test for, and close with alternatives (when not to use this approach).

Summary

You completed an advanced treatment of Liskov Substitution Principle (LSP). Revisit after building a feature that uses it end-to-end; spaced repetition with real code beats re-reading alone.