chart-item-id-equality-test

Arguments: chart-widget

Returns the value of the chart-item-id-equality-test property of a chart-widget. The value may be set at creation time by passing the :chart-item-id-equality-test initarg, or any time later by calling (setf chart-item-id-equality-test).

The value of this property is a function (or a the name of a function) that should return true if two chart item ID's are equivalent. The function is used whenever a chart value is being looked up from its item ID, to test whether each ID is the one that is sought.

The default value is equal, which should suffice for ordinary types of chart item ID's such as symbols, numbers, and strings. If all of the ID's are symbols, for example, then it may improve efficiency a bit to specify eq as the value of this property.

Chart item IDs are established by calls to set-chart-value or by a chart-value-returner function.

See also chart-object-id-equality-test.

See chart-widget and also cg-chart-widget.htm.

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Created 2019.8.20.