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#### 23.2.2.14 Xmethod API

The GDB Python API provides classes, interfaces and functions to implement, register and manipulate xmethods. See Xmethods In Python.

An xmethod matcher should be an instance of a class derived from `XMethodMatcher` defined in the module `gdb.xmethod`, or an object with similar interface and attributes. An instance of `XMethodMatcher` has the following attributes:

Variable: name

  The name of the matcher.

Variable: enabled

  A boolean value indicating whether the matcher is enabled or disabled.

Variable: methods

  A list of named methods managed by the matcher. Each object in the list is an instance of the class `XMethod` defined in the module `gdb.xmethod`, or any object with the following attributes:

  `name`

    Name of the xmethod which should be unique for each xmethod managed by the matcher.

  `enabled`

    A boolean value indicating whether the xmethod is enabled or disabled.

  The class `XMethod` is a convenience class with same attributes as above along with the following constructor:

  Function: XMethod.__init__ (self, name)

    Constructs an enabled xmethod with name name.

The `XMethodMatcher` class has the following methods:

Function: XMethodMatcher.__init__ (self, name)

  Constructs an enabled xmethod matcher with name name. The `methods` attribute is initialized to `None`.

Function: XMethodMatcher.match (self, class_type, method_name)

  Derived classes should override this method. It should return a xmethod worker object (or a sequence of xmethod worker objects) matching the class_type and method_name. class_type is a `gdb.Type` object, and method_name is a string value. If the matcher manages named methods as listed in its `methods` attribute, then only those worker objects whose corresponding entries in the `methods` list are enabled should be returned.

An xmethod worker should be an instance of a class derived from `XMethodWorker` defined in the module `gdb.xmethod`, or support the following interface:

Function: XMethodWorker.get_arg_types (self)

  This method returns a sequence of `gdb.Type` objects corresponding to the arguments that the xmethod takes. It can return an empty sequence or `None` if the xmethod does not take any arguments. If the xmethod takes a single argument, then a single `gdb.Type` object corresponding to it can be returned.

Function: XMethodWorker.get_result_type (self, *args)

  This method returns a `gdb.Type` object representing the type of the result of invoking this xmethod. The args argument is the same tuple of arguments that would be passed to the `__call__` method of this worker.

Function: XMethodWorker.__call__ (self, *args)

  This is the method which does the work of the xmethod. The args arguments is the tuple of arguments to the xmethod. Each element in this tuple is a gdb.Value object. The first element is always the `this` pointer value.

For GDB to lookup xmethods, the xmethod matchers should be registered using the following function defined in the module `gdb.xmethod`:

Function: register_xmethod_matcher (locus, matcher, replace=False)

  The `matcher` is registered with `locus`, replacing an existing matcher with the same name as `matcher` if `replace` is `True`. `locus` can be a `gdb.Objfile` object (see Objfiles In Python), or a `gdb.Progspace` object (see Progspaces In Python), or `None`. If it is `None`, then `matcher` is registered globally.

Next: Writing an Xmethod, Previous: Xmethods In Python, Up: Python API [Contents][Index]