check

functional, fluent and extensible validation toolkit for Go.

This library is under active development, feature PRs are welcomed

Goals

When validating large objects with sophisticated business logic and intertwined value dependencies, imperative programming often makes it hard to tell the actual logic underneath, thus making it hard to maintain. To add salt to injury, Go's verbose error handling makes it even harder to maintain.

This project aims at providing a validation API that is almost fluent in natural language, composable to represent sophisticated logic, and extensible wherever the defaults fall short.

In addition, with the assumption that the validation code already knows how the validated value should be like, this library would try to stay away from reflection as much as possible, while having a minimal API surface area.

Install

go get -u github.com/imulab/check

Main Concepts

The library is designed with minimal API surface, it has only a few concepts:

1. check.Step is the core concept, it takes in any interface{} value with assumed type, and applies validation to it. It returns an error when validation fails.
2. check.Skip is the special error to be returned by check.Step, to skip all remaining steps.
3. check.That is the main entrypoint for validation, it accepts multiple check.Step to execute sequentially.
4. check.AnyErr can chain multiple check.That together to eagerly return any error.

Usage

// Check str variable is not empty.
check.That(str, stringz.IsNotEmpty)

// Check str is "a" or "b", as long as it is not empty. If str is
// not "a" and "b", return a customErr.
check.That(str,
    check.Optional.When(stringz.IsEmpty),
    stringz.In("a", "b").Err(customErr),
)

// Check all elements of the string slice is "a", "b", or "c", or
// return a customErr.
check.That(slice,
    slicez.OfString.All(stringz.In("a", "b", "c")),
).Err(customErr)