Implement first-class callable syntax

[thekid]

Examples

// Old code without checks whether any of these are actually callable
$length= function(... $args) { return strlen(...$args); };
$run= function(... $args) use($instance) { return $instance->run(...$args); };
$of= function(... $args) { return Enum::valueOf(...$args); };

// Old code, requires PHP 7.1
$length= Closure::fromCallable('strlen');
$run= Closure::fromCallable([$instance, 'run']);
$of= Closure::fromCallable([Enum::class, 'valueOf']);

// Now possible, works on all PHP versions w/ XP Compiler
$length= strlen(...);
$run= $instance->run(...)
$of= Enum::valueOf(...);

See also

• https://wiki.php.net/rfc/closurefromcallable
• https://wiki.php.net/rfc/first_class_callable_syntax
• first class callable conversion php/php-src#7019
• Implement first-class callable syntax ast#27

[thekid]

Once the RFC merged to PHP 8.1, we should move this to a trait for PHP 7.4 and 8.0 and emit native code on PHP 8.1

[thekid]

Now the only thing we need to do is to remove the use CallablesAsClosures from the PHP81 emitter.

[thekid]

This implementation does not check for and subsequently disallow nullsafe calls as described in the PHP RFC, leaving it up to the runtime engine. This could be added easily (see below), however, it would be a first in the emitter, which doesn't throw errors up until now!

diff --git a/src/main/php/lang/ast/emit/PHP.class.php b/src/main/php/lang/ast/emit/PHP.class.php
index 3a10a60..ba460e9 100755
--- a/src/main/php/lang/ast/emit/PHP.class.php
+++ b/src/main/php/lang/ast/emit/PHP.class.php
@@ -1,5 +1,6 @@
 <?php namespace lang\ast\emit;

+use lang\IllegalStateException;
 use lang\ast\Code;
 use lang\ast\nodes\{InstanceExpression, ScopeExpression, BinaryExpression, Variable, Literal, ArrayLiteral, Block};
 use lang\ast\types\{IsUnion, IsFunction, IsArray, IsMap};
@@ -989,6 +990,10 @@ abstract class PHP extends Emitter {
   }

   protected function emitCallable($result, $callable) {
+    if ($callable->expression->kind === 'nullsafeinstance') {
+      throw new IllegalStateException('Cannot use ?-> with callables');
+    }
+
     $t= $result->temp();
     $result->out->write('fn(...'.$t.') => ');
     $this->emitOne($result, $callable->expression);

[thekid]

This can safely be merged, the vote is at 41:0 in favor of including this and thus very unlikely to fail.

[thekid]

Released in https://github.com/xp-framework/compiler/releases/tag/v6.7.0

[thekid]

Updated https://github.com/xp-framework/compiler/wiki/Implementation-status