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Date:2009-05-25T20:38:08.000000Z git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@227 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
84 lines
4.3 KiB
Plaintext
84 lines
4.3 KiB
Plaintext
[[Property:title|Converting EiffelVision 2 Systems to Void Safety]]
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[[Property:link_title|Converting EiffelVision 2 Systems to Void-Safety]]
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[[Property:weight|1]]
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[[Property:uuid|96e01318-700b-da6e-42d1-14fee219daf5]]
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Converting EiffelVision 2 System to Void Safety
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In order to convert systems that employ EiffelVision 2 (Vision2) to void-safety, some adjustments may be needed depending on its usage. This document describes the various usage scenarios of Vision2 that will need converting to adhere to void-safety.
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Inheritance purely from an Interface Class
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If you have classes that inherit from a Vision2 interface class such as EV_DRAWING_AREA, the first change that has to be made is to alter 'initialize' so that any types that are attached (ie: types that remain non-void throughout the lifetime of its housing parent object) are initialized via 'create_interface_objects', this needs to be redefined if the type from Vision2 is instantiable, if not then it may need to be made effective (such as inheritance directly from EV_ANY). It is important that any attached types in the interface class are instantiated in `create_interface_objects' and these objects are initialized via 'initialize'. Attached types should not be instantiated in `initialize' due to the bridge pattern implementation and initialization of these types in `create_interface_objects' MUST be performed via 'initialize', otherwise unexpected behavior may occur as the bridge pattern has not been fully set up at this point in time.
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Example from EV_TIMEOUT
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feature {NONE} -- Implementation
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create_interface_objects
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-- <Precursor>
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do
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create actions
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end
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create_implementation
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-- Create implementation of button.
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do
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create {EV_TIMEOUT_IMP} implementation.make
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end
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Inheritance from an Implementation Interface Class with associating interface class
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If you have an existing, custom platform dependent implementation, there are a few more changes needed than what was required for the interface class.
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For the interface class changes, now the interface object is passed to the implementation after creation, via `assign_interface', this means that `make' no longer takes an argument. This also means that to adhere to void-safety all of the types are now created and initialized via the creation routine of the implementation object.
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An example from the conversion of Windows implementation of EV_BUTTON_IMP.
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make (an_interface: like interface)
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-- Create `Current' with interface `an_interface'.
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do
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base_make (an_interface)
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wel_make (default_parent, "", 0, 0, 0, 0, 0)
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extra_width := 20
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text_alignment := default_alignment
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-- Retrieve the theme for the button.
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open_theme := application_imp.theme_drawer.open_theme_data (wel_item, "Button")
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end
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initialize
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-- Initialize `Current'.
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do
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Precursor {EV_PRIMITIVE_IMP}
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set_default_font
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end
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interface: EV_BUTTON;
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would become:
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make
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-- Initialize `Current'.
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do
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wel_make (default_parent, "", 0, 0, 0, 0, 0)
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extra_width := 20
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text_alignment := default_alignment
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-- Retrieve the theme for the button.
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open_theme := application_imp.theme_drawer.open_theme_data (wel_item, "Button")
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Precursor {EV_PRIMITIVE_IMP}
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set_default_font
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end
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interface: detachable EV_BUTTON note option: stable attribute end;
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The following steps are needed during the conversion:
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- The attribute 'interface' needs to be made a stable attribute
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- Copy any initialization of the widget from 'make' to 'initialize' excluding `base_make' setup. Any initialization code that relies on `interface' would have to be rewritten so that this gets passed to new creation routine that in turn calls the original `make'. See EV_PRINT_PROJECTOR_IMP on Windows `make_with_context' for an example of this.
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- Remove `make', rename `initialize' to `make', make sure that any calls to Precursor do not override any settings set in 'initialize', the ordering may need to be changed in order to make the code void-safe so. See EV_POPUP_WINDOW_IMP.make (Windows implementation) where the setting of 'user_can_resize' is performed after the Precursor call so that is doesn't get overriden.
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