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Help/command/variable_watch.rst
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Petr Kmoch
Help: Expand documentation of variable_watch()
09 июл 2020, 18:22
09 июл 2020, 18:22
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variable_watch -------------- Watch the CMake variable for change. .. code-block:: cmake variable_watch(<variable> [<command>]) If the specified ``<variable>`` changes and no ``<command>`` is given, a message will be printed to inform about the change. If ``<command>`` is given, this command will be executed instead. The command will receive the following arguments: ``COMMAND(<variable> <access> <value> <current_list_file> <stack>)`` ``<variable>`` Name of the variable being accessed. ``<access>`` One of ``READ_ACCESS``, ``UNKNOWN_READ_ACCESS``, ``MODIFIED_ACCESS``, ``UNKNOWN_MODIFIED_ACCESS``, or ``REMOVED_ACCESS``. The ``UNKNOWN_`` values are only used when the variable has never been set. Once set, they are never used again during the same CMake run, even if the variable is later unset. ``<value>`` The value of the variable. On a modification, this is the new (modified) value of the variable. On removal, the value is empty. ``<current_list_file>`` Full path to the file doing the access. ``<stack>`` List of absolute paths of all files currently on the stack of file inclusion, with the bottom-most file first and the currently processed file (that is, ``current_list_file``) last. Note that for some accesses such as :command:`list(APPEND)`, the watcher is executed twice, first with a read access and then with a write one. Also note that an :command:`if(DEFINED)` query on the variable does not register as an access and the watcher is not executed. Only non-cache variables can be watched using this command. Access to cache variables is never watched. However, the existence of a cache variable ``var`` causes accesses to the non-cache variable ``var`` to not use the ``UNKNOWN_`` prefix, even if a non-cache variable ``var`` has never existed.