[Swig-devel] [ swig-Bugs-1794247 ] csbase typemap should only affect base classes

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Bugs item #1794247, was opened at 2007-09-13 13:58
Message generated for change (Comment added) made by qwertie
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Category: csharp
Group: None
Status: Closed
Resolution: Invalid
Priority: 5
Private: No
Submitted By: David Piepgrass (qwertie)
Assigned to: William Fulton (wsfulton)
Summary: csbase typemap should only affect base classes

Initial Comment:
An unnecessary warning comes out of this code:

%typemap(csbase) SWIGTYPE "CppWrapper"
class A {};
class B : public A{};

1>swig.i(59): Warning(833): Warning for B proxy: Base CppWrapper ignored. Multiple inheritance is not supported in C#.

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>Comment By: David Piepgrass (qwertie)
Date: 2007-10-19 16:11

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I'm not following. Why would somebody want 'B' to have any base class
other than 'A'? Even if a warning is appropriate, I think it should be a
different warning... something like 'Warning: Base CppWrapper will not be
used on derived classes unless you use the replace="1" flag on the csbase
typemap'

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Comment By: William Fulton (wsfulton)
Date: 2007-10-19 15:55

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There is a bug when using %typemap(csbase, replace="1") on derived classes
which generated uncompileable code. This is fixed now and is the solution
you can use to remove that warning. The warning is intentional as it
highlight a particular potential problem in the commonly used scenario of
giving all proxy classes a common pure C# base. See new testcase
inherit_target_language.i.

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Comment By: David Piepgrass (qwertie)
Date: 2007-10-02 16:06

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What? Come on, think about it for a minute. The csbase typemap, as its
name implies, affects only the C# base class, not the C++ base class. In my
C++ code I only use single inheritance and in the C# code I obviously
intend to use single inheritance. Clearly, the csbase typemap should only
apply to A, not B. Giving that warning in this situation is just silly. It
should be reserved for cases of C++ code that has multiple base classes.

Or look at it this way. You have these pairs of typemaps: csinterfaces and
csinterfaces_derived; csbody and csbody_derived. Why do you have these
separate typemaps? It's because base classes and derived classes have
different needs. Likewise in this case. I would suggest there should be
csbase and csbase_derived typemaps too, except that csbase_derived has no
reason to exist, and that just leaves csbase.


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Comment By: William Fulton (wsfulton)
Date: 2007-10-02 14:20

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You have explicitly added an additional base class to B so the warning is
correct. If you don't like it, then suppress it, eg:

%warnfilter(833) B;
or
%warnfilter(833);

or use the warning name, eg
%warnfilter(SWIGWARN_CSHARP_MULTIPLE_INHERITANCE);

Also note the replace attribute which will replace the real base class
with this one:
%typemap(csbase, replace="1") SWIGTYPE "CppWrapper"

Also if CppWrapper is an interface, use csinterfaces instead:
%typemap(csinterfaces) SWIGTYPE "CppWrapper"
%typemap(csinterfaces_derived) SWIGTYPE "CppWrapper"


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