docs(type) Provides an initial documentation document for the Type co…

…mponent

src/Psl/Type/README.md

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+# Type
+
+## Introduction
+
+The type component provides a set functions to ensure that a given value is of a specific type.
+It aims to provide a solution for the [Parse, Don't Validate](https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-validate/) problem.
+
+## Usage
+
+```php
+use Psl;
+use Psl\Type;
+
+$untrustedInput = $request->get('input');
+
+// Turns a string-like value into a non-empty-string
+$trustedInput = Type\non_empty_string()->coerce($untrustedInput);
+
+// Or assert that its already a non-empty-string
+$trustedInput = Type\non_empty_string()->assert($untrustedInput);
+
+// Or check if its a non-empty-string
+$isTrustworthy = Type\non_empty_string()->matches($untrustedInput);
+```
+
+Every type provided by this component is an instance of `Type\TypeInterface<Tv>`.
+This interface provides the following methods:
+
+- `matches(mixed $value): $value is Tv` - Checks if the provided value is of the type.
+- `assert(mixed $value): Tv` - Asserts that the provided value is of the type or throws an `AssertException` on failure.
+- `coerce(mixed $value): Tv` - Coerces the provided value into the type or throws a `CoercionException` on failure.
+
+
+## API
+
+### Functions
+
+<div class="api-functions">
+
+* [`Type\converted<I, 0>(TypeInterface<I> $from, TypeInteface<O>, (Closure(I): O)): TypeInterface<O>` php]
+
+  Provides a type `O` that can be converted from a type `I` using a converter function.
+
+  ```php
+  <?php
+  use Psl\Type;
+
+  $dateTimeType = Type\converted(
+    Type\string(),
+    Type\instance_of(DateTimeImmutable::class),
+    static function (string $value): DateTimeImmutable {
+        $date = DateTimeImmutable::createFromFormat('Y-m-d H:i:s', $value);
+        if (!$date) {
+            // Exceptions will be transformed to CoerceException
+            throw new \RuntimeException('Invalid format given. Expected date to be of format {format}');
+        }
+
+        return $date;
+    }
+  );
+
+  $emailType = Type\converted(
+    Type\string(),
+    Type\instance_of(EmailValueObject::class),
+    static function (string $value): EmailValueObject {
+        // Exceptions will be transformed to CoerceException
+        return EmailValueObject::tryParse($value);
+    }
+  );
+
+  $shape = Type\shape([
+    'email' => $emailType,
+    'dateTime' => $dateTimeType
+  ]);
+
+  // Coerce will convert from -> into, If the provided value is already into - it will skip conversion.
+  $coerced = $shape->coerce($data);
+
+  // Assert will check if the value is of the type it converts into! 
+  $shape->assert($coerced); 
+  ```
+
+  This type can also be used to transform array-shaped values into custom Data-Transfer-Objects:
+
+  ```php
+  use Psl\Type;
+  use Psl\Type\TypeInterface;
+
+  /**
+   * @psalm-immutable
+   */
+  final class Person {
+
+      public function __construct(
+          public readonly string $firstName,
+          public readonly string $lastName,
+      ) {
+      }
+
+      /**
+       * @pure
+       *
+       * @return TypeInterface<self>
+       */
+      public static function type(): TypeInterface {
+          return Type\converted(
+              Type\shape([
+                  'firstName' => Type\string(),
+                  'lastName' => Type\string(),
+              ]),
+              Type\instance_of(Person::class),
+              fn (array $data): Person => new Person(
+                  $data['firstName'],
+                  $data['lastName']
+              )
+          );
+      }
+
+      /**
+       * @pure
+       */
+      public static function parse(mixed $data): self
+      {
+          return self::type()->coerce($data);
+      }
+  }
+
+  // The Person::type() function can now be used as its own type so that it can easily be reused throughout your application.
+
+  $nested = Type\shape([
+      'person' => Person::type(),
+  ]);
+  ```
+
+* [`Type\shape<Tk of array-key, Tv>(dict<Tv, Tk> $elements, bool $allow_unknown_fields = false): TypeInterface<array<Tk, Tv>>` php]
+
+  Provides a type that can parse (deeply nested) arrays. A shape can consist out of multiple child-shapes and structures:
+
+  ```php
+  use Psl\Type;
+
+  $shape = Type\shape([
+      'name' => Type\string(),
+      'articles' => Type\vec(Type\shape([
+          'title' => Type\string(),
+          'content' => Type\string(),
+          'likes' => Type\int(),
+          'comments' => Type\optional(
+              Type\vec(Type\shape([
+                  'user' => Type\string(),
+                  'comment' => Type\string()
+              ]))
+          ),
+      ])),
+      'dictionary' => Type\dict(Type\string(), Type\vec(Type\shape([
+          'title' => Type\string(),
+          'content' => Type\string(),
+      ]))),
+      'pagination' => Type\optional(Type\shape([
+          'currentPage' => Type\uint(),
+          'totalPages' => Type\uint(),
+          'perPage' => Type\uint(),
+          'totalRows' => Type\uint(),
+      ]))
+  ]);
+
+  $validData = $shape->coerce([
+      'name' => 'ok',
+      'articles' => [
+          [
+              'title' => 'ok',
+              'content' => 'ok',
+              'likes' => 1,
+              'comments' => [
+                  [
+                      'user' => 'ok',
+                      'comment' => 'ok'
+                  ],
+                  [
+                      'user' => 'ok',
+                      'comment' => 'ok',
+                  ]
+              ]
+          ]
+      ],
+      'dictionary' => [
+          'key' => [
+              [
+                  'title' => 'ok',
+                  'content' => 'ok',
+              ]
+          ]
+      ]
+  ]);
+  ```
+
+  When the data structure does not match the specified shape, you will get detailed information about what went wrong exactly:
+
+  > Expected "array{'name': string, 'articles': vec<array{'title': string, 'content': string, 'likes': int, 'comments'?: vec<array{'user': string, 'comment': string}>}>, 'dictionary': dict<string, vec<array{'title': string, 'content': string}>>, 'pagination'?: array{'currentPage': uint, 'totalPages': uint, 'perPage': uint, 'totalRows': uint}}", got "array" at path **"articles.0.comments.0"**.
+  
+</div>