A partial porting of io-ts in PHP

0.0.3 2022-01-16 17:51 UTC


PHP-codec is a partial porting of io-ts in PHP.

Minimum PHP Version

CI Static analysis codecov Join the chat at https://gitter.im/php-codec/community

Install it now. It only requires PHP >= 7.4.

composer require facile-it/php-codec


This project is under active development: it's unstable and still poorly documented. The API is likely to change several times, and it won't be ready for production soon.

The project follows semantic versioning.


This project is a partial porting of the fantastic io-ts library for Typescript. Everything rounds about the concept of decoder, encoder and codec.

Decoders are capable of transform values from one type to another one. This transformation may fail.

use Facile\PhpCodec\Validation\Validation;

 * @psalm-template I
 * @psalm-template A
interface Decoder {
     * @psalm-param I $i
     * @psalm-return Validation<A>
    public function decode($i): Validation;
    /** ... */

Encoders do a similar transformation but between types such that it cannot fail.

 * @psalm-template A
 * @psalm-template O
interface Encoder
     * @psalm-param A $a
     * @psalm-return O
    public function encode($a);

Codecs are a combination of a decoder and an encoder, putting together their features.

I recommend reading the The Idea section from the documentation of io-ts. It starts with a beautiful description of what codecs are.

A value of type Type<A, O, I> (called "codec") is the run time representation of the static type A.

Getting started

composer require facile-it/php-codec


Decoders are objects with decoding capabilities. A decoder of type Decoder<I, A> takes an input of type I and builds a result of type Validation<A>.

The class Facile\PhpCodec\Decoders provides factory methods for built-in decoders and combinators.

How to use decoders

use Facile\PhpCodec\Decoders;
use Facile\PhpCodec\Decoder;
use Facile\PhpCodec\Validation\Validation;
use Facile\PhpCodec\Validation\ValidationFailures;
use Facile\PhpCodec\Validation\ValidationSuccess;

/** @var Decoder<string, int> $decoder */
$decoder = Decoders::intFromString();

/** @var Validation<int> $v1 */
$v1 = $decoder->decode('123');
// Since '123' is a numeric string which represents an integer,
// then we can expect the decoding to be successful.
// Hence, $v1 will be an instance of ValidationSuccess

if($v1 instanceof ValidationSuccess) {

/** @var Validation<int> $v2 */
$v2 = $decoder->decode('hello');
// Similarly, since 'hello' is not a numeric string, we expect 
// the decoding fail. $v2 will be an instance of ValidationError

if($v2 instanceof ValidationFailures) {

Dealing with the validation result

We can use Validation::fold to destruct the validation result while providing a valid result in any case.

use Facile\PhpCodec\Decoders;
use Facile\PhpCodec\Decoder;
use Facile\PhpCodec\Validation\Validation;

/** @var Decoder<string, int> $decoder */
$decoder = Decoders::intFromString();

    function (\Facile\PhpCodec\Validation\ValidationFailures $failures): int {
        // I may not care about the error.
        // Here I want to give a default value when the deconding fails.
        return 0;
    function (\Facile\PhpCodec\Validation\ValidationSuccess $success): int {
        return $success->getValue();

You can use the path reporter to build well-formatted error messages for failures.

use Facile\PhpCodec\Decoders;

$decoder = Decoders::intFromString();
$v = $decoder->decode('hello');
$msgs = \Facile\PhpCodec\Reporters::path()->report($v);

/* This will print 
array(1) {
  [0] =>
  string(49) "Invalid value "hello" supplied to : IntFromString"


Take a look to the examples folder.


Reporters do create reports from Validation objects. Generally speaking, reporters are objects that implement the Reporter<T> interface, given T the type of the report that the generate.

One interesting group of reporters is the validation error reporters group. They implements Reporter<list<string>>. Thus, given a Validation object, they generate a list of error messages for each validation error.

PHP-Codec comes with two error reporters:

  • PathReporter, which is a pretty straightforward porting of io-ts' PathReporter.
  • SimplePathReporter, which is a simplified (read: shorter messages) version of the PathReporter.
$d = Decoders::arrayProps([
  'a' => Decoders::arrayProps([
    'a1' => Decoders::int(),
    'a2' => Decoders::string(),
  'b' => Decoders::arrayProps(['b1' => Decoders::bool()])
$v = $d->decode(['a'=> ['a1' => 'str', 'a2' => 1], 'b' => 2]);

$x = \Facile\PhpCodec\Reporters::path()->report($v);
// $x will be
// ['Invalid value "str" supplied to : {a: {a1: int, a2: string}, b: {b1: bool}}/a: {a1: int, a2: string}/a1: int',
//  'Invalid value 1 supplied to : {a: {a1: int, a2: string}, b: {b1: bool}}/a: {a1: int, a2: string}/a2: string',
//  'Invalid value undefined supplied to : {a: {a1: int, a2: string}, b: {b1: bool}}/b: {b1: bool}/b1: bool']

$y = \Facile\PhpCodec\Reporters::simplePath()->report($v);
// $y will be
// ['/a/a1: Invalid value "str" supplied to decoder "int"',
//  '/a/a2: Invalid value 1 supplied to decoder "string"',
//  '/b/b1: Invalid value undefined supplied to decoder "bool"']