Philosophy

In this package a validation rule is called a Constraint.

All constraints are immutable objects. This means that you can compose them any way you want safely.

Unlike most validation packages, here you can directly apply transformation on each validated value (1). This brings 2 benefits:

1. via the ->map() methods

• no need to write ifs after validation when transforming the data to please static analysis tools
• no need to have classes that look like valid data just to declare validations rules

This helps have a clear separation between declaring the expected structure (1) and the execution.

1. both the input and the output

Another benefit of contraints being immutable objects is that there's no central validator object. This means that anyone can create its own Constraint and use it directly.