Hi list,
as a response to recent discussion on the mailing list, I finally got
around to writing the PSEP draft for defining the behaviour when
overloaded signals are connected. Please see below and comment whether
the behaviour is something you'd like to have or whether the PSEP would
need to be changed.
Cheers,
ma.
PSEP: 105
Title: Connecting overloaded signals
Version: $Revision$
Last-Modified: $Date$
Author: Matti Airas <[email protected]>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 23-Nov-2010
Post-History: 23-Nov-2010
Abstract
========
This PSEP further clarifies PSEP 100 [#psep0100]_ by defining that when
connecting a signal with an overloaded signature, you have to explicitly
define the signature, unless a void signature exists.
Rationale
=========
It is common in Qt for a signal to have several overloaded signatures.
For example, QtGui.QComboBox.activated has alternative ``int`` and
``unicode`` signatures.
A specific signature may be defined as shown in the example below::
self.cbox.activated[unicode].connect(myfunc)
In addition to specifying an explict signature, the existing PySide--as
well as PyQt--syntax allows for default signatures to be used by just
omitting the signature when connecting signals::
self.cbox.activated.connect(myfunc)
The default signatures in both PySide and PyQt are defined in
implementation only, and there already exist incompatibilities between
PySide and PyQt in this regard. Since using the default signatures may
lead to obscure errors and undefined behaviour, explicit signatures are
to be preferred.
Explicit signatures are required
================================
This PSEP defines that if the signal has overloaded signatures, the
explicit signature must be defined when connecting signals to slots. If
the signature is omitted, an exception will be raised.
Empty signatures are still mapped to default signatures
-------------------------------------------------------
As an exception to the rule above, if the signal supplies a void
signature, this is mapped to the default signature. For example, in the
case of ``QPushButton``, both ``clicked()`` and ``clicked(bool)`` are
supported. To connect to the void signature, it is sufficient to use::
self.mybutton.clicked.connect(myfunc)
while the ``bool`` signature still requires the explicit definition:
self.mybutton.clicked[bool].connect(myfunc)
Discussion
==========
The issue was first raised in a PySide bug report [#bug327]_. After
that, the issue was discussed on the PySide mailing list [#ml20101021]_.
The general opinion was that explicit signatures are to be preferred.
The first PSEP draft was written using that discussion as the guideline.
Compatibility
=============
This PSEP introduces a small backwards-incompatible change. Since the
change is minor and only affects behaviour that should be considered
undefined, the implementation will be done before PySide 1.0 release.
References
==========
.. [#psep0100] PSEP 100: New-style Signals and Slots, Airas
(http://www.pyside.org/docs/pseps/psep-0100.html)
.. [#bug327] PySide Bug 327
(http://bugs.openbossa.org/show_bug.cgi?id=327)
.. [#ml20101021] Mailing list discussion: Default signal signature used
in connection, Renato Filho
(http://lists.openbossa.org/pipermail/pyside/2010-October/001206.html)
Contributors
============
Renato Filho proposed the semantics specified in this PSEP.
Copyright
=========
This document has been placed in the public domain.
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