Find out what type my class is being converted to for comparisons
I am in the process of building a matrix class (uni project, with
my choice of programming language) and appear to have run into a
problem that I'm not too sure how to fix.
My class uses templates to define the shape of the matrix,
although I'm not sure if that matters. As part of my class, I
included a opEquals, but when I try to assert that a matrix
created by multiplying with the identity matrix matches the
output (I checked with liberal writeln()s to make sure they do)
but my opEquals() function (I moved it out of the class as I kept
getting errors saying it was supposed to be non-const, and
couldn't figure out how to fix that either) just isn't called.
---
Matrix code (the only bit of the class used by opEquals):
```
class Matrix(size_t X, size_t Y = X){
const size_t x_length = X;
const size_t y_length = Y;
double[X*Y] data;
...
}
```
The entirety of opEquals:
```
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X,Y) m1, const
Matrix!(X,Y) m2) {
for (int i = 0; i < m1.data.length; ++i) if (m1.data[i] !=
m2.data[i]) return false;
return true;
}
```
and the code that excepts:
```
void main() {
auto m = new Matrix!(2)();
m.data = [1.0,0.0,0.0,1.0].dup;
auto n = new Matrix!(2)();
n.data = [2.0,3.0,4.0,5.0].dup;
auto u = mult(m,n);
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
// using opEquals() directly is working, but it doesn't
seem to be being used
//assert(opEquals(u,n),"\"opEquals(u, n)\" is failing.");
// this works fine
assert(u == n,"\"u == n\" is failing."); // this fails.
Why?
}
```
---
Any help would be very much appreciated. A way to figure out what
the '==' is converting its arguments to would also be great, but
I'm not sure it exists (beyond just sitting down and trying to
work it out myself, of course)
Re: Find out what type my class is being converted to for comparisons
Well its not a type system issue.
Making u = n, that'll returns true.
So the problem almost certainly lies with IEEE-754.
They are horrible to compare (float/double).
Unfortunately you are stuck calling functions like isClose to compare.
https://dlang.org/phobos/std_math_operations.html#.isClose
Full code extracted from above:
```d
import std;
void main()
{
auto m = new Matrix!(2)();
m.data = [1.0, 0.0, 0.0, 1.0].dup;
auto n = new Matrix!(2)();
n.data = [2.0, 3.0, 4.0, 5.0].dup;
auto u = mult(m, n);
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
// using opEquals() directly is working, but it doesn't seem to be
being used
//assert(opEquals(u,n),"\"opEquals(u, n)\" is failing."); // this
works fine
assert(u == n, "\"u == n\" is failing."); // this fails. Why?
}
class Matrix(size_t X, size_t Y = X)
{
const size_t x_length = X;
const size_t y_length = Y;
double[X * Y] data;
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X, Y) m1, const
Matrix!(X, Y) m2)
{
for (int i = 0; i < m1.data.length; ++i)
if (m1.data[i] != m2.data[i])
return false;
return true;
}
}
```
Re: Find out what type my class is being converted to for comparisons
On Tuesday, 18 October 2022 at 18:59:37 UTC, rikki cattermole wrote: Well its not a type system issue. Making u = n, that'll returns true. So the problem almost certainly lies with IEEE-754. They are horrible to compare (float/double). Unfortunately you are stuck calling functions like isClose to compare. https://dlang.org/phobos/std_math_operations.html#.isClose Hi Rikki, thanks for the rapid reply. I'm not so sure it isn't a type issue, tbh. The only reason being that the opEquals() works whenever I call it directly (ignoring the comparison of proximity to a value for the moment) but doesn't work when I use "==" stripped down to just the two lines that are causing issues: ``` //assert(opEquals(u,n)); // this works fine assert(u == n); // this fails. Why? ``` I guess to put it more bluntly, I should ask "why is opEquals working when I call it directly, but when I try to use the equality check, which should be CALLING opEquals, it doesn't appear to do so?"
Re: Find out what type my class is being converted to for comparisons
On Tuesday, 18 October 2022 at 18:53:41 UTC, Matthew Rushworth
wrote:
The entirety of opEquals:
```
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X,Y) m1, const
Matrix!(X,Y) m2) {
for (int i = 0; i < m1.data.length; ++i) if (m1.data[i] !=
m2.data[i]) return false;
return true;
}
```
A free-standing opEquals won't work. It needs to be a method of
the class. So:
```d
class Matrix(size_t X, size_t Y = X)
{
/* ... */
bool opEquals(const Matrix m2)
{
for (int i = 0; i < this.data.length; ++i)
if (this.data[i] != m2.data[i]) return false;
return true;
}
}
```
Re: Find out what type my class is being converted to for comparisons
On Tuesday, 18 October 2022 at 20:02:02 UTC, ag0aep6g wrote:
On Tuesday, 18 October 2022 at 18:53:41 UTC, Matthew Rushworth
wrote:
The entirety of opEquals:
```
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X,Y) m1, const
Matrix!(X,Y) m2) {
for (int i = 0; i < m1.data.length; ++i) if (m1.data[i] !=
m2.data[i]) return false;
return true;
}
```
A free-standing opEquals won't work. It needs to be a method of
the class. So:
```d
class Matrix(size_t X, size_t Y = X)
{
/* ... */
bool opEquals(const Matrix m2)
{
for (int i = 0; i < this.data.length; ++i)
if (this.data[i] != m2.data[i]) return false;
return true;
}
}
```
Thank you, that worked perfectly, not sure exactly what I did
wrong, I'm assuming I forgot to make the parameter a const
variable
Re: Find out what type my class is being converted to for comparisons
On 10/19/22 00:43, Matthew Rushworth via Digitalmars-d-learn wrote: Thank you, that worked perfectly, not sure exactly what I did wrong, I'm assuming I forgot to make the parameter a const variable Object, the root of the class object hierarchy already defines an opEquals [1] and you need to overload/overwrite that for it to work properly. Only class methods are considered, hence ag0aep6g's suggestion. [1] https://dlang.org/library/object/object.op_equals.html
Re: Find out what type my class is being converted to for comparisons
On Tuesday, 18 October 2022 at 18:53:41 UTC, Matthew Rushworth
wrote:
I am in the process of building a matrix class (uni project,
with my choice of programming language) and appear to have run
into a problem that I'm not too sure how to fix.
My class uses templates to define the shape of the matrix,
although I'm not sure if that matters. As part of my class, I
included a opEquals, but when I try to assert that a matrix
created by multiplying with the identity matrix matches the
output (I checked with liberal writeln()s to make sure they do)
but my opEquals() function (I moved it out of the class as I
kept getting errors saying it was supposed to be non-const, and
couldn't figure out how to fix that either) just isn't called.
---
Matrix code (the only bit of the class used by opEquals):
```
class Matrix(size_t X, size_t Y = X){
const size_t x_length = X;
const size_t y_length = Y;
double[X*Y] data;
...
}
```
The entirety of opEquals:
```
/// both matrices have to have an identical shape to compare
/// each element must be identical to match
bool opEquals(size_t X, size_t Y)(const Matrix!(X,Y) m1, const
Matrix!(X,Y) m2) {
for (int i = 0; i < m1.data.length; ++i) if (m1.data[i] !=
m2.data[i]) return false;
return true;
}
```
and the code that excepts:
```
void main() {
auto m = new Matrix!(2)();
m.data = [1.0,0.0,0.0,1.0].dup;
auto n = new Matrix!(2)();
n.data = [2.0,3.0,4.0,5.0].dup;
auto u = mult(m,n);
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
// using opEquals() directly is working, but it doesn't
seem to be being used
//assert(opEquals(u,n),"\"opEquals(u, n)\" is
failing."); // this works fine
assert(u == n,"\"u == n\" is failing."); // this fails.
Why?
}
```
---
Any help would be very much appreciated. A way to figure out
what the '==' is converting its arguments to would also be
great, but I'm not sure it exists (beyond just sitting down and
trying to work it out myself, of course)
What's the reason for it being a class? struct makes more sense
here, plus it'll be faster
If it were a struct, you'd not need any of that, and you can also
have operator overloading for your mult while also being able to
check how many row/col at compile time, here an example:
```D
import std;
struct Matrix(size_t X, size_t Y = X)
{
enum x_length = X; // enum so it's available only at compile
time
enum y_length = Y;
double[X * Y] data;
// operator overloading
Matrix opBinary(string op)(Matrix rhs)
{
static if (op == "*")
{
//
// ** ADD YOUR MULT OPERATION HERE **
//
static if (X == 2)
{
return Matrix();
}
else
static assert("not supported");
}
else
static assert(0, "Operator " ~ op ~ " not
implemented");
}
}
void main()
{
// check equality by value:
auto a = Matrix!(2)();
a.data = 0;
auto b = Matrix!(2)();
b.data = 0;
writeln("are they the same?: ", a == b); // it'll check for
equality by value
auto m = Matrix!(2)();
m.data = [1.0, 0.0, 0.0, 1.0];
auto n = Matrix!(2)();
n.data = [2.0, 3.0, 4.0, 5.0];
// here we can use the * operator!
auto u = m * n;
writeln("u.data vs n.data:");
for (int i = 0; i < u.data.length; ++i)
writeln(u.data[i], "\t", n.data[i]);
}
```
