Parse, Don’t Validate

When handling data in software development, ensuring its validity is essential. The "Parse don’t validate" principle provides a robust approach by encouraging developers to transform data into specific types that guarantee correctness, rather than merely checking it and proceeding with raw, potentially unsafe data.

What is "Parse, Don’t Validate"?

Instead of validating data (e.g., checking if it meets certain criteria) and then using it in its original form, parsing converts data into a type that inherently enforces its validity. Once parsed, you can trust the data throughout your application without needing repeated checks.

Let’s say you’re working with a user’s age. A validation approach might look like this:

However, with "Parse, don’t validate," you’d create a dedicated Age type:

"Parse, don’t validate" ensures data integrity by transforming raw input into strongly-typed objects that enforce correctness, eliminating the need for repeated validation checks throughout the codebase. This approach reduces errors and enhances maintainability by centralizing constraints within the type system, making code safer and easier to reason about.