4.4.3.3 Operations on Properties

Function: list properties (obj object)

Returns a list of the names of the properties defined directly on the given object, not inherited from its parent. If object is not valid, then E_INVARG is raised. If the programmer does not have read permission on object, then E_PERM is raised.

Function: list property_info (obj object, str prop-name)

Function: none set_property_info (obj object, str prop-name, list info)

These two functions get and set (respectively) the owner and permission bits for the property named prop-name on the given object. If object is not valid, then E_INVARG is raised. If object has no non-built-in property named prop-name, then E_PROPNF is raised. If the programmer does not have read (write) permission on the property in question, then property_info() (set_property_info()) raises E_PERM. Property info has the following form:

{owner, perms [, new-name]}

where owner is an object, perms is a string containing only characters from the set `r', `w', and `c', and new-name is a string; new-name is never part of the value returned by property_info(), but it may optionally be given as part of the value provided to set_property_info(). This list is the kind of value returned by property_info() and expected as the third argument to set_property_info(); the latter function raises E_INVARG if owner is not valid, if perms contains any illegal characters, or, when new-name is given, if prop-name is not defined directly on object or new-name names an existing property defined on object or any of its ancestors or descendants.

Function: none add_property (obj object, str prop-name, value, list info)

Defines a new property on the given object, inherited by all of its descendants; the property is named prop-name, its initial value is value, and its owner and initial permission bits are given by info in the same format as is returned by property_info(), described above. If object is not valid or info does not specify a valid owner and well-formed permission bits or object or its ancestors or descendants already defines a property named prop-name, then E_INVARG is raised. If the programmer does not have write permission on object or if the owner specified by info is not the programmer and the programmer is not a wizard, then E_PERM is raised.

Function: none delete_property (obj object, str prop-name)

Removes the property named prop-name from the given object and all of its descendants. If object is not valid, then E_INVARG is raised. If the programmer does not have write permission on object, then E_PERM is raised. If object does not directly define a property named prop-name (as opposed to inheriting one from its parent), then E_PROPNF is raised.

Function: int is_clear_property (obj object, str prop-name)

Function: none clear_property (obj object, str prop-name)

These two functions test for clear and set to clear, respectively, the property named prop-name on the given object. If object is not valid, then E_INVARG is raised. If object has no non-built-in property named prop-name, then E_PROPNF is raised. If the programmer does not have read (write) permission on the property in question, then is_clear_property() (clear_property()) raises E_PERM. If a property is clear, then when the value of that property is queried the value of the parent's property of the same name is returned. If the parent's property is clear, then the parent's parent's value is examined, and so on. If object is the definer of the property prop-name, as opposed to an inheritor of the property, then clear_property() raises E_INVARG.