Modules: Introduction

Modules are an experimental feature for organizing code and separating your internal and external APIs. Modules are collections of Hack files that share an identity or utility.

Module definitions

You can define a new module with the new module keywords.

//// module.hack
new module foo {}

Modules do not share a namespace with other symbols. Module names can contain periods . to help delineate between directories or logical units. Periods in module names do not currently have any semantic meaning.

//// module_foo.hack
new module foo {}
//// module_foobar.hack
new module foo.bar {}
//// module_foobartest.hack
new module foo.bar.test {}

Module membership

Any Hack file can be placed in a defined module by writing module <module name> at the top of the file.

module foo;
class Foo {
  // ...
}

Module level visibility: internal

By placing your code in modules, you can use a new visibility keyword: internal. An internal symbol can only be accessed from within the module.

//// foo_class.hack
module foo;

public class Foo {}
internal class FooInternal {
  public function foo(): void {}
  internal function bar(): void {}
}
internal function foo_fun(): void {}

An internal symbol cannot be accessed outside of the module it's defined in.

module bar;

public function bar_test(): void {
  $x = new FooInternal(); // error! FooInternal is internal to module foo.
}