godot-docs/tutorials/scripting/c_sharp/diagnostics/GD0203.rst

GD0203: The delegate signature of the signal must return void
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                                      Value
====================================  ======================================
**Rule ID**                           GD0203
**Category**                          Usage
**Fix is breaking or non-breaking**   Breaking - If the return type is changed

                                      Non-breaking - If the ``[Signal]`` attribute is removed
**Enabled by default**                Yes
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Cause
-----

A delegate annotated with the ``[Signal]`` attribute has a return type when
``void`` was expected.

Rule description
----------------

Every signal must return ``void``. There can be multiple callbacks registered
for each signal, if signal callbacks could return something it wouldn't be
possible to determine which of the returned values to use.

.. code-block:: csharp

    // This signal delegate is invalid because it doesn't return void.
    public int InvalidSignalEventHandler();

    // This signal delegate is valid because it returns void.
    public void ValidSignalEventHandler();

Take a look at the :ref:`C# signals <doc_c_sharp_signals>` documentation for more
information about how to declare and use signals.

How to fix violations
---------------------

To fix a violation of this rule, change the delegate to return ``void`` or
remove the ``[Signal]`` attribute from the delegate. Note that removing the
attribute will mean the signal is not registered.

.. tip::

    If the signal doesn't need to interact with Godot, consider using
    `C# events <https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/events/>`_
    directly. Pure C# events allow you to use any C# type for its parameters.

When to suppress warnings
-------------------------

Do not suppress a warning from this rule. Signal delegates that return something
will result in unexpected runtime errors.