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zend_attribute.rst

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zend_attribute

PHP attributes are stored in a dedicated structure zend_attribute, which holds details of attributes.

definition

typedef struct _zend_attribute {
    zend_string *name;
    zend_string *lcname;
    uint32_t flags;
    uint32_t lineno;
    /* Parameter offsets start at 1, everything else uses 0. */
    uint32_t offset;
    uint32_t argc;
    zend_attribute_arg args[1];
} zend_attribute;

Broadly, the attribute holds

  • the name of the attribute (name, lcname)
  • metadata about the attribute (flags)
  • metadata about the attribute usage (lineno, offset)
  • details of arguments (argc, args)

name

The name of the attribute is stored in the :doc:`./zend_string` name. To make case-insensitive comparisons easier, a lowercase version of the name is also saved in the :doc:`./zend_string` lcname.

flags

The flags field holds metadata about the internal details of how the attribute should be used. The flags are made from

#define ZEND_ATTRIBUTE_PERSISTENT   (1<<0)
#define ZEND_ATTRIBUTE_STRICT_TYPES (1<<1)

And are not the same as the flags in Attribute::$flags.

metadata

The name holds a :doc:`zend_string` with the name of the constant, to allow searching for constants that have already been defined. This string is released when the constant itself is freed.

filename

The lineno field holds the line number that the attribute is used on, for use in error messages.

The offset field is only used for attributes on parameters, and indicates which parameter the attribute is applied to (since the attributes for a function's parameters are all stored together).

arguments

The number of arguments that are passed to the attribute is stored in the argc field. But, since attributes support the use of named parameters, storing just the parameters that were used is not enough, the parameter names need to be stored too.

Those are stored in zend_attribute_arg objects:

typedef struct {
    zend_string *name;
    zval value;
} zend_attribute_arg;

Where the name field stores the name used, and the :doc:`./zval` value field stores the value.