Callback Validator Laravel Package

daverandom/callback-validator

Validate PHP callable signatures against a prototype with variance support. Build a CallbackType from an existing callable or define it manually, then test other callables for parameter/return compatibility (contra/covariance, nullability) and inspect mismatches via __toString().

Product Decisions This Supports

Enables strict callback contract enforcement in plugin architectures and API integrations
Reduces runtime errors by validating user-provided callbacks against expected signatures
Provides a "buy" solution for specialized validation needs instead of custom implementation
Critical for roadmap items requiring type-safe event systems or hook-based extensions

When to Consider This Package

Adopt when building PHP 7+ libraries/frameworks requiring runtime callback signature validation
Ideal for systems where third-party callbacks must adhere to precise type contracts (e.g., event listeners, hooks)
Avoid if using static analysis tools alone (e.g., PHPStan), or when callback requirements are trivial/non-type-sensitive
Not suitable for projects without callback-based interfaces or those needing non-type-based validation logic

How to Pitch It (Stakeholders)

For executives: "Prevents costly production bugs by ensuring third-party callbacks conform to expected signatures, reducing support costs and improving system reliability. For engineering: integrates seamlessly via Composer with minimal performance overhead when cached, handles complex variance rules out-of-the-box, and eliminates manual signature validation logic—freeing teams to focus on core features."