README

This project defines a name-to-file resolution algorithm for autoloaders that allows more-than-one class per file.

Theory of Operation

One Class Per File

Historically, PHP class-to-file naming conventions have supported only one class per file.

Horde/PEAR

In the pre-namespacing versions of PHP, the original Horde/PEAR resolution logic converted underscores to directory separators to generate a file path:

Foo_Bar_Baz_Dib     => /classes/Foo/Bar/Baz/Dib.php
Foo_Bar_Baz_Dib_Zim => /classes/Foo/Bar/Baz/Dib/Zim.php

PSR-0

PSR-0 modified this logic to recognized the formal namespaces introduced in PHP 5.3, so that ...

1. namespace separators were converted to directory separators, and
2. underscores only in the terminating class name portion were converted to directory separators:

Foo_Bar\Baz\Dib     => /classes/Foo_Bar/Baz/Dib.php
Foo_Bar\Baz\Dib_Zim => /classes/Foo_Bar/Baz/Dib/Zim.php

PSR-4

PSR-4 modified PSR-0 so that ...

1. underscores in the terminating class name portion would no longer be converted to directory separators, and
2. a namespace prefix could be mapped to a directory prefix:

/**
 * Foo_Bar\Baz\ maps to /classes/foo-bar/baz/src/
 */
Foo_Bar\Baz\Dib     => /classes/foo-bar/baz/src/Dib.php
Foo_Bar\Baz\Dib_Zim => /classes/foo-bar/baz/src/Dib_Zim.php

More-Than-One Class Per File

The Moto name-to-file resolution algorithm modifies this even further, so that everything after an underscore in the terminating class name portion is ignored:

/**
 * Foo_Bar\Baz\ maps to /classes/foo-bar/baz/src/
 */
Foo_Bar\Baz\Dib     => /classes/foo-bar/baz/src/Dib.php
Foo_Bar\Baz\Dib_Zim => /classes/foo-bar/baz/src/Dib.php
Foo_Bar\Baz\Dib_Gir => /classes/foo-bar/baz/src/Dib.php
Foo_Bar\Baz\Dib_Irk => /classes/foo-bar/baz/src/Dib.php

This means the Dib.php file can contain any number of underscore-suffixed classes so long as they are prefixed with Dib ...

// /classes/foo-bar/src/Baz/Dib.php
namespace Foo_Bar/Baz;

class Dib { }

class Dib_Zim { }

class Dib_Gir { }

class Dib_Irk { }

... and a Moto-compliant resolver will find the correct file for that class.

Resolution Algorithm

Given ...

• a namespace-prefix of a non-empty namespace (including the rightmost namespace separator) or an empty string (indicating the global namespace), and

• an absolute directory-prefix for the namespace-prefix (including the rightmost directory separator)

... the following algorithm resolves a fully-qualified-name to an absolute-file-path or to null:

1. If the fully-qualified-name does not begin with the namespace-prefix, the fully-qualified-name resolves to null.

2. Otherwise, set the qualified-name by capturing all characters after the namespace-prefix.

3. If the qualified-name contains a namespace separator ...

   A. Set the partial-namespace by capturing all characters up to and including the rightmost namespace separator, and set the partial-name by capturing all characters after the rightmost namespace separator.

   B. Otherwise, set the partial-namespace to an empty string, and set the partial-name to the qualified-name.

4. If the partial-name contains an underscore, remove the first underscore and all characters thereafter.

5. If the partial-name is empty, the fully-qualified-name resolves to null.

6. Otherwise, set the partial-directory by converting each namespace separator in the partial-namespace to a DIRECTORY_SEPARATOR.

7. Set the absolute-file-path by concatenating the directory-prefix, partial-directory, partial-name, and a filename-suffix (typically .php).

8. If the absolute-file-path exists, the fully-qualified-name resolves to the absolute-file-path; otherwise, it resolves to null.

Cf. the reference implementation resolutionAlgotrithm() method for an example.

Implications

• Directory names with underscores WILL be resolvable.

• Base file names with underscores WILL NOT be resolvable.

• PSR-4 mapped classes without underscores are Moto-compatible.

• The partial-name itself does not have to exist at the absolute-file-path; that is, the file might contain only underscore-suffixed names:

  // Foo_Bar\Baz => /vendor/foo-bar/baz/src/Dib.php
  namespace Foo_Bar\Baz;
  
  // no Dib {} class
  
  class Dib_Zim {}
  
  class Dib_Gir {}
  
  class Dib_Irk {}

• If function autoloading becomes supported by PHP, the Moto name-to-file resolution algorithm can support multiple functions per file:

  // Foo_Bar\Baz => /vendor/foo-bar/baz/src/dib.php
  namespace Foo_Bar\Baz;
  
  function dib() {}
  
  function dib_zim() {}
  
  function dib_gir() {}
  
  function dib_irk() {}