Templated compositors

[Michael Hopkins]

Hi all

I'm trying to create compositors (as described in TCPPPL 3rd edition 22.4.7)
for expressing the matrix multiplication function:

mat_mult( a, b, result );

As this:

result = a * b;
I have defined the compositor structure like this:
================================================== =========================

In "matrix.hpp"which contains:
template <typename T> class Mat { ....
--------------------------------------------------------------
struct MMmul;

Mat( const MMmul& mm ) { mat_mult( this, &m.m1, &m.m2 ); }

Mat& operator=( const MMmul& mm ) {
mat_mult( this, &m.m1, &m.m2 );
return *this;
}
In "la_operations.hpp" which includes "matrix.hpp"
--------------------------------------------------
struct MMmul {
Mat<double> const & m1;
Mat<double> const & m2;

MMmul( const Mat<double>& mm1, const Mat<double>& mm2 ) : m1(mm1), m2(mm2)
{}

operator Mat<double>();
};

inline
MMmul operator* ( const Mat<double> & m1, const Mat<double> & m2 ) {
return MMmul( m1, m2 );
}

================================================== =========================

It all compiles OK when used with some Mat<double> objects, but fails the
link with this:

ld: Undefined symbols:
MMmul::operator Mat<double>()

Any thoughts gratefully received - please also cc to my email.

TIA

Michael
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[Rolf Magnus]

Michael Hopkins wrote:

It all compiles OK when used with some Mat<double> objects, but fails the
link with this:

ld: Undefined symbols:
MMmul::operator Mat<double>()

Well, in the code fragments you posted, that operator is only declared, not
defined. The error message suggests that this is also the case in your real
code.
Btw: I don't know why you would define such an operator, since you already
have the corresponding conversion constructor in Mat.
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[Thomas Maier-Komor]

Michael Hopkins wrote:

Hi all

I'm trying to create compositors (as described in TCPPPL 3rd edition 22.4.7)
for expressing the matrix multiplication function:

mat_mult( a, b, result );

As this:

result = a * b;
I have defined the compositor structure like this:
================================================== =========================

In "matrix.hpp"which contains:
template <typename T> class Mat { ....
--------------------------------------------------------------
struct MMmul;

Mat( const MMmul& mm ) { mat_mult( this, &m.m1, &m.m2 ); }

Mat& operator=( const MMmul& mm ) {
mat_mult( this, &m.m1, &m.m2 );
return *this;
}
In "la_operations.hpp" which includes "matrix.hpp"
--------------------------------------------------
struct MMmul {
Mat<double> const & m1;
Mat<double> const & m2;

MMmul( const Mat<double>& mm1, const Mat<double>& mm2 ) : m1(mm1), m2(mm2)
{}

operator Mat<double>();
};

inline
MMmul operator* ( const Mat<double> & m1, const Mat<double> & m2 ) {
return MMmul( m1, m2 );
}

================================================== =========================

It all compiles OK when used with some Mat<double> objects, but fails the
link with this:

ld: Undefined symbols:
MMmul::operator Mat<double>()

Any thoughts gratefully received - please also cc to my email.

TIA

Michael

Well, just as it says: you declare "MMmul::operator Mat<double>()", but
as far as I can see from what you posted, there does not seem to be a
definition of this method...

Tom

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[Michael Hopkins]

On 17/5/05 3:01 pm, in article d6************@news.t-online.com, "Rolf
Magnus" <ra******@t-online.de> wrote:

Michael Hopkins wrote:

It all compiles OK when used with some Mat<double> objects, but fails the
link with this:

ld: Undefined symbols:
MMmul::operator Mat<double>()
Well, in the code fragments you posted, that operator is only declared, not
defined. The error message suggests that this is also the case in your real
code.

Thanks to Rolf and Thomas for pointing out the same thing here. It was 2am
when I finally gave up! ;o)

Does anyone have a suggestion for what the definition of MMmul::operator
Mat<double>() should be and where it should be put? I am feeling a little
tentative as I enter the world of C++ from a C background.
Btw: I don't know why you would define such an operator, since you already
have the corresponding conversion constructor in Mat.

I have commented it out and now get this compilation error:

error: no matching function for call to `mat_mult(const hr::Mat<double>*,
const hr::Mat<double>*, hr::Mat<double>* const)'
candidates are:
void hr::mat_mult(const hr::Mat<double>&, const hr::Mat<double>&,
hr::Mat<double>&)

So now it seems the compiler has implied a signature of:

const Mat<T>*, const Mat<T>*, Mat<T>* const

For the call to mat_mult( const Mat<T>&, const Mat<T>&, Mat<T>& ) in here:

Mat & operator= ( const MMmul & m ) {
mat_mult( &m.m1, &m.m2, this );
return *this;
}

I am running out of knowledge - is this a problem that I can deal with by a
cast of some kind, is there a more elegant solution or am I doing something
fundamentally wrong? I cannot clarify this from BS's code where he
introduces the technique.

Michael
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_/ _/ _/_/_/ Hopkins Research Ltd
_/ _/ _/ _/
_/_/_/_/ _/_/_/ http://www.hopkins-research.com/
_/ _/ _/ _/
_/ _/ _/ _/ 'touch the future'

_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/

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[Rolf Magnus]

Michael Hopkins wrote:

On 17/5/05 3:01 pm, in article d6************@news.t-online.com, "Rolf
Magnus" <ra******@t-online.de> wrote:

Michael Hopkins wrote:

It all compiles OK when used with some Mat<double> objects, but fails
the link with this:

ld: Undefined symbols:
MMmul::operator Mat<double>()

Well, in the code fragments you posted, that operator is only declared,
not defined. The error message suggests that this is also the case in
your real code.

Thanks to Rolf and Thomas for pointing out the same thing here. It was 2am
when I finally gave up! ;o)

Does anyone have a suggestion for what the definition of MMmul::operator
Mat<double>() should be and where it should be put? I am feeling a little
tentative as I enter the world of C++ from a C background.

My point was that you don't need it. Mat<double>Mat::( const MMmul&  mm )
already does the conversion.

Btw: I don't know why you would define such an operator, since you
already have the corresponding conversion constructor in Mat.

I have commented it out and now get this compilation error:

error: no matching function for call to `mat_mult(const hr::Mat<double>*,
const hr::Mat<double>*, hr::Mat<double>* const)'
candidates are:
void hr::mat_mult(const hr::Mat<double>&, const hr::Mat<double>&,
hr::Mat<double>&)

So now it seems the compiler has implied a signature of:

const Mat<T>*, const Mat<T>*, Mat<T>* const

For the call to mat_mult( const Mat<T>&, const Mat<T>&, Mat<T>& ) in here:

Mat & operator= ( const MMmul & m ) {
mat_mult( &m.m1, &m.m2, this );
return *this;
}

That's no surprise - at least not to me ;-)
m.m1 is a const Mat<double>, so &m.m1 is a pointer to const Mat<double>.
Same for &m.m2. and 'this' is also a pointer to Mat<double>, though not
const in this case. Try:

mat_mult(m.m1, m.m2, *this);
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