Class Constants

This chapter covers how to define a class constant.

Note that more in dept details about constants are covered in the constants chapter.

Code sample for this chapter, with additional examples, is available here.

Userland PHP Code Snippet

The code below shows how a class constant would be declared in userland PHP code.

class Hdi {
  public const HELLO = 'World!';
}

Internal PHP Code

The following sections show all required code to declare and implement a class constant internally in PHP.

PHP Stub (hdi.stub.php)

The stub file should not declare class constants as the stub generator script (gen_stub.php) cannot handle it at this moment.

Argument Information (hdi_arginfo.h)

Class constants are not referred to nor registered in the argument information file, so it can be skipped.

Implementation (hdi.c)

The implementation below is a little bit more elaborate than what is seen in global scope constant, but it can be broken into:

  • name definition (zend_string_init)
    • name string ("HELLO")
    • name size (sizeof)
    • persistent string (0 ie. not persistent1)
  • value definition (ZVAL_NEW_STR and zend_string_init)
    • value string ("World!")
    • value size (sizeof)
    • persistent string (depends if classEntry->type is a ZEND_INTERNAL_CLASS or not)
  • declaration (zend_declare_class_constant_ex)
    • class entry (classEntry)
    • visibility (ZEND_ACC_PRIVATE)
zend_string *name = zend_string_init(
  "HELLO",
  sizeof("HELLO") - 1,
  0
);

zval value;
ZVAL_NEW_STR(
  &value,
  zend_string_init(
    "World!",
    sizeof("World!") - 1,
    classEntry->type & ZEND_INTERNAL_CLASS
  )
);

zend_declare_class_constant_ex(
  classEntry,
  name,
  &value,
  ZEND_ACC_PRIVATE,
  NULL
);
zend_string_release(name);

Alternatively, for public class constants, it can be simplified as:

zend_declare_class_constant_string(
  classEntry,
  "HELLO",
  sizeof("HELLO") - 1,
  "World!"
);

Macros and Functions:

Visibility options:

Notes:

1

More about persistent objects in the Zend Memory Manager chapter of the PHP Internals Book.

Copyright (c) 2022 - Flavio Heleno