added Printer::printArrowFunction()

Author: dg

readme.md

@@ -335,6 +335,27 @@ function ($a, $b) use (&$c) {
 }
 ```
 
+Arrow function
+--------------
+
+You can also print closure as arrow function using printer:
+
+```php
+$closure = new Nette\PhpGenerator\Closure;
+$closure->setBody('return $a + $b;');
+$closure->addParameter('a');
+$closure->addParameter('b');
+
+// or use PsrPrinter for output compatible with PSR-2 / PSR-12
+echo (new Nette\PhpGenerator\Printer)->printArrowFunction($closure);
+```
+
+Result:
+
+```php
+fn ($a, $b) => $a + $b;
+```
+
 Method and Function Body Generator
 ----------------------------------
 

src/PhpGenerator/Printer.php

@@ -61,6 +61,22 @@ public function printClosure(Closure $closure): string
 	}
 
 
+	public function printArrowFunction(Closure $closure): string
+	{
+		foreach ($closure->getUses() as $use) {
+			if ($use->isReference()) {
+				throw new Nette\InvalidArgumentException('Arrow function cannot bind variables by-reference.');
+			}
+		}
+
+		return 'fn '
+			. ($closure->getReturnReference() ? '&' : '')
+			. $this->printParameters($closure, null)
+			. $this->printReturnType($closure, null)
+			. ' => ' . trim($closure->getBody()) . ';';
+	}
+
+
 	public function printMethod(Method $method, PhpNamespace $namespace = null): string
 	{
 		$method->validate();

tests/PhpGenerator/Printer.arrow.phpt

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+use Nette\PhpGenerator\Closure;
+use Nette\PhpGenerator\Printer;
+use Tester\Assert;
+
+
+require __DIR__ . '/../bootstrap.php';
+
+
+$function = new Closure;
+$function
+	->setReturnReference(true)
+	->setBody('$a + $b');
+
+$function->addParameter('a');
+$function->addParameter('b');
+
+Assert::same('fn &($a, $b) => $a + $b;', (new Printer)->printArrowFunction($function));
+
+
+
+$function = new Closure;
+$function
+	->setReturnType('array')
+	->setBody('[]');
+
+Assert::same('fn (): array => [];', (new Printer)->printArrowFunction($function));
+
+
+Assert::exception(function () {
+	$function = new Closure;
+	$function->addUse('vars')
+		->setReference(true);
+	(new Printer)->printArrowFunction($function);
+}, Nette\InvalidArgumentException::class, 'Arrow function cannot bind variables by-reference.');