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
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 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
