Re: swig and C# bindings, was: "swig and java bindings"

[Paul Gentry(INTERN)]

I'm trying to use part of Quantlib in C#, but the swig interface seems
incomplete.  I followed a thread about a similar problem using QuantLib
with Java, and I've quoted part of a message from that thread below.

I believe I'm having the same issues as the Java people, so I'm working
on fixing the linearalgebra.i interface to the Matrix class, in order to
use it with C#.  I think I've got something working, but I thought I
would post this in case anyone else is working on the same thing and/or
encounters the same issues.

So here are some questions, comments, and a tip to solve a problem I
encountered:

Questions:
1) Why is the SWIG interface for the Matrix class defined in a file
called linearalgebra.i rather than a file called Matrix.i or Matrix.swg?

2) Why do they use .i files instead of .swg files?  Wouldn't it be more
clear that .swg files are SWIG files, to a developer new to SWIG?

3) In the swig/java thread, Luigi Ballabio was kind enough to offer some
sample code to create SWIG bindings, he said:

> You'll have to edit the corresponding SWIG interface file, namely,
> linearalgebra.i, regenerate the wrappers, and recompile.
> As for the edit, you have to add the methods you want to the Matrix
> interface, e.g.,
>
> class Matrix {
> ...
> #if defined(SWIGJAVA)
> Array get(int i) {
> Array a(self->columns());
> std::copy(self->row_begin(i), self->row_end(i), a.begin());
> return a;
> }
> Matrix multiply(Matrix m) {
> return *self * m;
> }
> ...
> #endif
> ...
> };
>

I believe I understand this code for the most part, but I wasn't sure
why get returns an entire row of the matrix, and isn't used to just get
one cell?  Is it related to efficiency/speed?

Comment/Opinion:
Regarding the QuantLib C++ code here, it seems like self->columns()
should be called self->numColumns().  I expect a method called
self->columns() to return a set of columns (which I guess would be a
Matrix) rather than the number of columns.

Tip:
For those who might be building the SWIG bindings on Windows: I couldn't
figure out how to make the Quantlib-SWIG/CSharp project re-build the
swig bindings.  I tried by re-building each part of the QuantLib-SWIG
project (in Visual Studio) using "Rebuild All" and rebuilding the
Solution using "Rebuild All", but that did not re-build the swig
bindings.  So, after a long and frustrating search and several futile
attempts, I managed to discover the magic incantation to re-build the
swig bindings on the command line.  At first, I kept getting the error
that "swig.swg" and other files were not found -- i.e. it couldn't find
the main swig library directory.  First I tried adding it to the Windows
PATH, but that didn't help.  Eventually I figured out how to tell swig
where the swig libraries are: you have to set an environment variable
called SWIG_LIB by doing something like the following:
set SWIG_LIB=[your path here]\swigwin-1.3.31\Lib

This isn't the recommended method according to the documentation, but
since I don't know what ./configure is, and I don't have mingw or minw
or whatever it is, I couldn't run ./configure and I'm not sure that
would have done much for me anyway.  (And installing all that to do
something 'relatively simple' seems like a huge hassle.)

cheers,
Paul G.

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[Luigi Ballabio]

On Thu, 2007-09-27 at 16:31 -0400, Paul Gentry(INTERN) wrote:
> I'm trying to use part of Quantlib in C#, but the swig interface seems
> incomplete.  I followed a thread about a similar problem using QuantLib
> with Java, and I've quoted part of a message from that thread below.
>
> I believe I'm having the same issues as the Java people, so I'm working
> on fixing the linearalgebra.i interface to the Matrix class, in order to
> use it with C#.  I think I've got something working, but I thought I
> would post this in case anyone else is working on the same thing and/or
> encounters the same issues.

Paul,
        are you willing to contribute the updated bindings?


> So here are some questions, comments, and a tip to solve a problem I
> encountered:
>
> Questions:
> 1) Why is the SWIG interface for the Matrix class defined in a file
> called linearalgebra.i rather than a file called Matrix.i or Matrix.swg?

Because it contains interfaces for both Array and Matrix. It's called
after the subdomain it's exporting.


> 2) Why do they use .i files instead of .swg files?  Wouldn't it be more
> clear that .swg files are SWIG files, to a developer new to SWIG?

It seemed to be the existing practice among SWIG developers.


> 3) In the swig/java thread, Luigi Ballabio was kind enough to offer some
> sample code to create SWIG bindings, he said:
> [...]
> I believe I understand this code for the most part, but I wasn't sure
> why get returns an entire row of the matrix, and isn't used to just get
> one cell?  Is it related to efficiency/speed?

No, it was just the interface requested by the poster I was replying to.
One can just as easily export get(i,j) if it's more idiomatic C#.


> Tip:
> For those who might be building the SWIG bindings on Windows: I couldn't
> figure out how to make the Quantlib-SWIG/CSharp project re-build the
> swig bindings.

It's done externally, by running the included swig.cmd script. You're
right, this should be documented.

> I kept getting the error
> that "swig.swg" and other files were not found -- i.e. it couldn't find
> the main swig library directory.  First I tried adding it to the Windows
> PATH, but that didn't help.  Eventually I figured out how to tell swig
> where the swig libraries are: you have to set an environment variable
> called SWIG_LIB by doing something like the following:
> set SWIG_LIB=[your path here]\swigwin-1.3.31\Lib

Strange---as long as the Lib folder is in the same location as the SWIG
executable (swig.exe) it should pick it up automatically---at least it
does on my machine.

> This isn't the recommended method according to the documentation, but
> since I don't know what ./configure is, and I don't have mingw or minw
> or whatever it is, I couldn't run ./configure and I'm not sure that
> would have done much for me anyway.  (And installing all that to do
> something 'relatively simple' seems like a huge hassle.)

True---configure only applies to Linux or MinGW.  You're better off your
way on a Windows machine.

Thanks for the feedback,
        Luigi


--

Cogito ergo I'm right and you're wrong.
-- Blair Houghton



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