Re: Templated operator overloading
On Wednesday, 22 August 2018 at 12:36:39 UTC, Simen Kjærås wrote: Since both your opOpAssigns match equally, the compiler throws up. The solution is to add some sort of restriction: This doesn't happen apparently: the operator has a left and a right side, even if both types define the operator, only one of them is on the left at each call. It works now after Ali corrected my stupid syntax :)
Re: Templated operator overloading
On Wednesday, 22 August 2018 at 13:20:01 UTC, aliak wrote: "void opOpAssign(string op, T)(ref Tthis, const ref T x)" looks like the wrong signature for opOpAssign. Oh I'll put on my stupid hat now... I realize I had copy-pasted the wrong syntax from the global function attempt, but I swear I thought I had re-typed and tested the right one... It's working now :)
Re: Templated operator overloading
On Wednesday, 22 August 2018 at 11:58:25 UTC, XavierAP wrote:
I've been trying some things to template operator overloads.
The reason is that I want very similar code for different
types, but I can't use polymorphism, as they're structs rather
than classes. Perhaps this choice is not as advantageous as I
think, and I may change this design from structs to classes, or
else the code duplication would be small and never subject to
change. But now I'm just trying for the sake of learning to
find out what works or not in terms of templated operator
overloading, and whether the reason something doesn't work is
by design and if mentioned in the specification, or just an
arbitraty result of some unspecified parsing/lowering step
order, or it depends on the compiler (I'm using dmd).
[...]
"void opOpAssign(string op, T)(ref Tthis, const ref T x)" looks
like the wrong signature for opOpAssign. THink it needs to be:
void opOpAssign(string op, T)(const ref T x)
Then:
mixin template operator!
{
void opOpAssign(string op, T)(const ref T x)
{
writeln(this, op, x);
}
}
struct S1
{
mixin operator;
}
struct S2
{
mixin operator;
}
Cheers,
- Ali
Re: Templated operator overloading
On Wednesday, 22 August 2018 at 11:58:25 UTC, XavierAP wrote:
When I want to have the same operator overloading code in both
types however, I can't make it work:
From https://dlang.org/spec/operatoroverloading.html#binary:
"the one with the ‘better’ match is selected. It is an error for
both to equally match."
Since both your opOpAssigns match equally, the compiler throws
up. The solution is to add some sort of restriction:
struct S1 {
mixin opOver;
}
struct S2 {
mixin opOver;
}
mixin template opOver() {
auto opOpAssign(string op, T)(T rhs)
if (T.stringof > typeof(this).stringof) { // Here
import std.stdio;
writeln(this, op, rhs);
}
}
unittest {
S1 a;
S2 b;
a += b;
}
And a final try with a global templated function instead of a
mixin template:
//
private void opOpAssign(string op, Tthis, T)(ref Tthis that,
const ref T x)
This syntax would either enable the definition of operators on
builtin types that shouldn't have them, or be perceived as
inconsistent, so invasive operator overloading is used in D
instead.
--
Simen
Templated operator overloading
I've been trying some things to template operator overloads. The
reason is that I want very similar code for different types, but
I can't use polymorphism, as they're structs rather than classes.
Perhaps this choice is not as advantageous as I think, and I may
change this design from structs to classes, or else the code
duplication would be small and never subject to change. But now
I'm just trying for the sake of learning to find out what works
or not in terms of templated operator overloading, and whether
the reason something doesn't work is by design and if mentioned
in the specification, or just an arbitraty result of some
unspecified parsing/lowering step order, or it depends on the
compiler (I'm using dmd).
Since there are in my case two similar types (below just a
minimal dumb proof of concept), I want the operator(s) to work
within the same type, or also with the other. The following code
actually works, including type parameter inferrence, and const
ref to avoid struct copying:
//
import std.stdio;
struct S1
{
void opOpAssign(string op, T)(const ref T x)
{
writeln(this, op, x);
}
}
struct S2
{}
void main()
{
S1 s1;
S2 s2;
s1 *= s2;
}
//
When I want to have the same operator overloading code in both
types however, I can't make it work:
//
private mixin template operator(Tthis)
{
void opOpAssign(string op, T)(ref Tthis, const ref T x)
{
writeln(this, op, x);
}
}
struct S1
{
mixin operator!S1;
}
struct S2
{
mixin operator!S2;
}
void main()
{
S1 s1;
S2 s2;
s1 *= s2; // Error: s1 *= s2 is not a scalar
s1.opOpAssign!"*"(s2); // Error: template
test.S1.operator!(S1).opOpAssign cannot deduce function
}
//
And a final try with a global templated function instead of a
mixin template:
//
private void opOpAssign(string op, Tthis, T)(ref Tthis that,
const ref T x)
{
writeln(that, op, x);
}
struct S1
{}
struct S2
{}
void main()
{
S1 s1;
S2 s2;
s1 *= s2; // Error: s1 *= s2 is not a scalar
s1.opOpAssign!"*"(s2); // OK!
}
//
