diff --git a/src/main/php/lang/ast/emit/Local.class.php b/src/main/php/lang/ast/emit/Local.class.php
new file mode 100755
index 00000000..d90a7d5c
--- /dev/null
+++ b/src/main/php/lang/ast/emit/Local.class.php
@@ -0,0 +1,10 @@
+<?php namespace lang\ast\emit;
+
+class Local {
+  public $type, $byRef;
+
+  public function __construct($type, $byRef= false) {
+    $this->type= $type;
+    $this->byRef= $byRef;
+  }
+}
\ No newline at end of file
diff --git a/src/main/php/lang/ast/emit/PHP.class.php b/src/main/php/lang/ast/emit/PHP.class.php
index 163ff27b..fffaacce 100755
--- a/src/main/php/lang/ast/emit/PHP.class.php
+++ b/src/main/php/lang/ast/emit/PHP.class.php
@@ -18,7 +18,7 @@
   UnpackExpression,
   Variable
 };
-use lang\ast\types\{IsUnion, IsFunction, IsArray, IsMap, IsNullable, IsExpression};
+use lang\ast\types\{IsUnion, IsFunction, IsArray, IsMap, IsNullable, IsExpression, IsLiteral};
 use lang\ast\{Emitter, Node, Type, Result};
 
 abstract class PHP extends Emitter {
@@ -27,6 +27,7 @@ abstract class PHP extends Emitter {
   const CONSTANT= 2;
 
   protected $literals= [];
+  public $extensions= [];
 
   /**
    * Creates result
@@ -113,6 +114,24 @@ protected function constantType($type) {
     }
   }
 
+  /**
+   * Returns type for a given node
+   *
+   * @param  lang.ast.emit.Result $result
+   * @param  lang.ast.Node $node
+   * @return ?lang.ast.Type
+   */
+  protected function typeOf($result, $node) {
+    if ($node instanceof Variable) {
+      $local= $result->locals[$node->pointer] ?? null;
+      return $local ? $local->type : null;
+    } else if ($node instanceof Literal) {
+      if ('"' === $node->expression[0] || "'" === $node->expression[0]) return new IsLiteral('string');
+    }
+
+    return null; // TBI
+  }
+
   /**
    * Enclose a node inside a closure
    *
@@ -126,7 +145,7 @@ protected function enclose($result, $node, $signature, $static, $emit) {
     $capture= [];
     foreach ($result->codegen->search($node, 'variable') as $var) {
       if (isset($result->locals[$var->pointer])) {
-        $capture[$var->pointer]??= ($result->locals[$var->pointer] ? '&$' : '$').$var->pointer;
+        $capture[$var->pointer]??= ($result->locals[$var->pointer]->byRef ? '&$' : '$').$var->pointer;
       }
     }
     unset($capture['this']);
@@ -146,7 +165,7 @@ protected function enclose($result, $node, $signature, $static, $emit) {
     if ($capture) {
       $result->out->write('use('.implode(', ', $capture).')');
       foreach ($capture as $name => $variable) {
-        $result->locals[$name]= '&' === $variable[0];
+        $result->locals[$name]= $locals[$name];
       }
     }
 
@@ -299,7 +318,7 @@ protected function emitArray($result, $array) {
   }
 
   protected function emitParameter($result, $parameter) {
-    $result->locals[$parameter->name]= $parameter->reference;
+    $result->locals[$parameter->name]= new Local($parameter->type, $parameter->reference);
     $parameter->annotations && $this->emitOne($result, $parameter->annotations);
 
     // If we have a non-constant default and a type, emit a nullable type hint
@@ -341,7 +360,7 @@ protected function emitSignature($result, $signature, $use= null) {
     if ($use) {
       $result->out->write(' use('.implode(',', $use).') ');
       foreach ($use as $variable) {
-        $result->locals[ltrim($variable, '&$')]= '&' === $variable[0];
+        $result->locals[ltrim($variable, '&$')]= new Local(null, '&' === $variable[0]);
       }
     }
 
@@ -689,7 +708,7 @@ protected function emitProperty($result, $property) {
 
   protected function emitMethod($result, $method) {
     $locals= $result->locals;
-    $result->locals= ['this' => false];
+    $result->locals= ['this' => new Local(null, false)]; // FIXME: Type
     $meta= [
       DETAIL_RETURNS     => $method->signature->returns ? $method->signature->returns->name() : 'var',
       DETAIL_ANNOTATIONS => $method->annotations,
@@ -815,10 +834,10 @@ protected function emitOffset($result, $offset) {
     }
   }
 
-  protected function emitAssign($result, $target) {
+  protected function emitAssign($result, $target, $type= null) {
     if ($target instanceof Variable && $target->const) {
       $result->out->write('$'.$target->pointer);
-      $result->locals[$target->pointer]= false;
+      $result->locals[$target->pointer]= new Local($type, false);
     } else if ($target instanceof ArrayLiteral) {
       $result->out->write('[');
       foreach ($target->values as $pair) {
@@ -838,7 +857,7 @@ protected function emitAssign($result, $target) {
   }
 
   protected function emitAssignment($result, $assignment) {
-    $this->emitAssign($result, $assignment->variable);
+    $this->emitAssign($result, $assignment->variable, $this->typeOf($result, $assignment->expression));
     $result->out->write($assignment->operator);
     $this->emitOne($result, $assignment->expression);
   }
@@ -1146,10 +1165,18 @@ protected function emitCallableNew($result, $callable) {
   }
 
   protected function emitInvoke($result, $invoke) {
-    $this->emitOne($result, $invoke->expression);
-    $result->out->write('(');
-    $this->emitArguments($result, $invoke->arguments);
-    $result->out->write(')');
+    if (
+      ($invoke->expression instanceof InstanceExpression) &&
+      ($type= $this->typeOf($result, $invoke->expression->expression)) &&
+      ($extension= $this->extensions[$type->literal()][$invoke->expression->member->expression] ?? null)
+    ) {
+      $this->emitOne($result, $extension($invoke->expression->expression, $invoke->arguments));
+    } else {
+      $this->emitOne($result, $invoke->expression);
+      $result->out->write('(');
+      $this->emitArguments($result, $invoke->arguments);
+      $result->out->write(')');
+    }
   }
 
   protected function emitScope($result, $scope) {
diff --git a/src/test/php/lang/ast/unittest/emit/EmittingTest.class.php b/src/test/php/lang/ast/unittest/emit/EmittingTest.class.php
index bfbc0eaf..96b5a982 100755
--- a/src/test/php/lang/ast/unittest/emit/EmittingTest.class.php
+++ b/src/test/php/lang/ast/unittest/emit/EmittingTest.class.php
@@ -13,6 +13,7 @@ abstract class EmittingTest {
   private static $id= 0;
   private $cl, $language, $emitter, $output;
   private $transformations= [];
+  private $extensions= [];
 
   /**
    * Constructor
@@ -54,6 +55,18 @@ protected function transform($type, $function) {
     $this->transformations[]= $this->emitter->transform($type, $function);
   }
 
+  /**
+   * Register an extension.
+   *
+   * @param  string $type
+   * @param  [:var] $impl
+   * @return void
+   */
+  protected function extension($type, $impl) {
+    $this->emitter->extensions[$type]= $impl;
+    $this->extensions[]= $type;
+  }
+
   /**
    * Parse and emit given code
    *
@@ -131,5 +144,9 @@ public function tearDown() {
     foreach ($this->transformations as $transformation) {
       $this->emitter->remove($transformation);
     }
+
+    foreach ($this->extensions as $type) {
+      unset($this->emitter->extensions[$type]);
+    }
   }
 }
\ No newline at end of file
diff --git a/src/test/php/lang/ast/unittest/emit/ExtensionsTest.class.php b/src/test/php/lang/ast/unittest/emit/ExtensionsTest.class.php
new file mode 100755
index 00000000..a3f35054
--- /dev/null
+++ b/src/test/php/lang/ast/unittest/emit/ExtensionsTest.class.php
@@ -0,0 +1,74 @@
+<?php namespace lang\ast\unittest\emit;
+
+use lang\ast\nodes\{Literal, BinaryExpression, InvokeExpression};
+use test\{Assert, Before, Test, Values};
+
+class ExtensionsTest extends EmittingTest {
+
+  #[Before]
+  public function install() {
+
+    // See https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/extension,
+    // this is what we might parse this from as an idea:
+    //
+    // ```php
+    // abstract class StringExtensions {
+    //   extension(string) {
+    //     public function length(string $self) => strlen($self);
+    //     public function contains(string $self, string $needle) => false !== strpos($self, $needle);
+    //   }
+    // }
+    // ```
+    // 
+    // Single-expression methods would be inlined at call-site!
+    $this->extension('string', [
+      'length'   => function($self, $arguments) {
+        return new InvokeExpression(new Literal('strlen'), [$self]);
+      },
+      'contains' => function($self, $arguments) {
+        return new BinaryExpression(
+          new Literal('false'),
+          '!==',
+          new InvokeExpression(new Literal('strpos'), [$self, $arguments[0]])
+        );
+      }
+    ]);
+  }
+
+  #[Test]
+  public function literal() {
+    Assert::equals(4, $this->run('class %T {
+      public function run() {
+        return "Test"->length();
+      }
+    }'));
+  }
+
+  #[Test]
+  public function local() {
+    Assert::equals(4, $this->run('class %T {
+      public function run() {
+        $test= "Test";
+        return $test->length();
+      }
+    }'));
+  }
+
+  #[Test, Values([['', 0], ['Test', 4]])]
+  public function param_length($input, $expected) {
+    Assert::equals($expected, $this->run('class %T {
+      public function run(string $input) {
+        return $input->length();
+      }
+    }', $input));
+  }
+
+  #[Test, Values([['', false], ['Test', true]])]
+  public function param_contains($input, $expected) {
+    Assert::equals($expected, $this->run('class %T {
+      public function run(string $input) {
+        return $input->contains("Test");
+      }
+    }', $input));
+  }
+}
\ No newline at end of file