#993 SWIG fails to find const& typemaps in %template expansion


If SWIG is given the following code,

%typemap(ctype) SWIGTYPE*& "TESTING*&"
%typemap(ctype) const SWIGTYPE*& "const TESTING*&"
%typemap(cstype) SWIGTYPE *& "ref TESTING"
%typemap(cstype) const SWIGTYPE *& "TESTING"

class Foo{}; // optional
void Test1(const Foo*& x);

It works as it should: the const SWIGTYPE*& typemaps are used. However, if an equivalent function is produced using %template, the non-const SWIGTYPE *& typemaps are used instead, e.g.

template<class T> void Test2(const T& x);
%template(Test2) Test2<Foo*>;


  • David Piepgrass

    David Piepgrass - 2009-03-06

    I think this bug is biting me again. Having written typemaps that allow object pointers to be passed by-reference, when I try to make a wrapper for std::vector<MyClass*> (where MyClass is also wrapped by SWIG) certain methods like Add, Insert and setitem come out wrong in C#:

    public void Add(ref StringSearchResult x) { ...
    public void Insert(int index, ref StringSearchResult x) { ...
    private void setitem(int index, ref StringSearchResult val) { ...

    I believe this is because SWIG wrongly interprets "const T&" as "StringSearchResult*&" when expanding templates.

  • William Fulton

    William Fulton - 2010-04-02

    Note that in C++ the following two are identical types, likewise in SWIG:
    SWIGTYPE const*&
    const SWIGTYPE*&

    Replace the two cstype typemaps you gave with:

    %typemap(cstype) SWIGTYPE *& "ref TESTING"
    %typemap(cstype) SWIGTYPE const*& "TESTING1"
    %typemap(cstype) SWIGTYPE *const& "TESTING2"

    Test1 then uses "TESTING1" and Test2 uses "TESTING2". This is correct as Test2 is more correctly written as:

    template<class T> void Test2(T const& x) {}
    which when instantiated with T as Foo *, is really Test2(Foo *const&) and so will not match SWIGTYPE const*&.

    Incidentally, swig-2.0.0 is much improved in typemap debugging with the -debug-tmsearch and -debug-tmused options documented in the Typemaps section in Typemaps.html section. Currently not released, but available in svn.

    Some language modules in older versions also incorrectly had SWIGTYPE *& typemaps when these should have been SWIGTYPE *const&, corrected in 2.0.0. This fixes the C# vector wrappers of const pointers too.

  • William Fulton

    William Fulton - 2010-04-02
    • labels: --> code generation (general)
    • status: open --> closed-invalid

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