--- title: "The Liskov Substitution Principle does more than you think" url: https://daily.dev/posts/the-liskov-substitution-principle-does-more-than-you-think-4gmhomlkz source_url: https://buttondown.com/hillelwayne/archive/the-liskov-substitution-principle-does-more-than type: article source: "Computer Things" published: 2026-06-17T11:26:15.037Z updated: 2026-06-17T11:33:32.294Z tags: ["general-programming"] reading_time: 7 upvotes: 0 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The Liskov Substitution Principle does more than you think **[Computer Things](https://daily.dev/sources/hillelwayne)** · 7 min read · 0 upvotes · 0 comments ## Summary The Liskov Substitution Principle (LSP) is commonly understood as just the 'L' in SOLID, applying only to inheritance hierarchies. But the original Liskov-Wing paper's core insight — that subtypes must have weaker or equal preconditions and stronger or equal postconditions — applies far more broadly. Any time you substitute one function or code block for another (including API versioning and backward compatibility), the same contract rules apply. Making a required parameter optional weakens preconditions (safe), while making an optional parameter required strengthens them (breaking). The post also connects this to Hyrum's Law: any observable behavior can become an implicit postcondition that someone depends on, meaning even 'strengthening' a postcondition by adding new output fields can break callers who relied on the absence of those fields. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Liskov Substitution Principle](https://daily.dev/posts/liskov-substitution-principle-nt8k1h6hv) · Ruby Flow · 1 upvotes · 0 comments - [Liskov Substitution Principle C\#: Correct Inheritance Every Time](https://daily.dev/posts/liskov-substitution-principle-c-correct-inheritance-every-time-t6mye5vlw) · We Are .NET · 2 upvotes · 0 comments - [A SOLID Load of Bull](https://daily.dev/posts/a-solid-load-of-bull-hw6sdv1co) · Lobsters · 23 upvotes · 2 comments - [What SOLID Still Teaches Ruby Programmers](https://daily.dev/posts/what-solid-still-teaches-ruby-programmers-24ppwefj9) · RUBYLAND · 0 upvotes · 0 comments --- Tags: [#general-programming](https://daily.dev/tags/general-programming) [View this post on daily.dev](https://daily.dev/posts/the-liskov-substitution-principle-does-more-than-you-think-4gmhomlkz)