I have two structs, point and vec, in which I want to implement
some arithmetic operations.
The operations are:
```
point - point = vec
point + vec = point
```
Using mixin templates the code compiles but calling the
operations in the main causes an "incompatible type" Error:
```d
mixin template sum(T, R) {
R opBinary(string op)(T rhs) const
if (op == "+"){
return R(x + rhs.x, y + rhs.y, z + rhs.z);
}
}
mixin template diff(T, R) {
R opBinary(string op)(T rhs) const
if (op == "-") {
return R(x - rhs.x, y - rhs.y, z - rhs.z);
}
}
struct point{
float x, y, z;
mixin diff!(point, vec);
mixin sum!(vec, point);
}
struct vec{
float x, y, z;
}
void main(){
point p1 = {1,2,3}, p2 = {5,6,7};
vec v1 = p1-p2;
vec v2 = {2,-1,0};
point p3 = p1+v2;
}
```
The output of `dub run` is
```
Performing "debug" build using /usr/bin/dmd for x86_64.
query ~master: building configuration "application"...
source/app.d(27,13): Error: incompatible types for `(p1) - (p2)`:
both operands are of type `point`
source/app.d(30,15): Error: incompatible types for `(p1) + (v2)`:
`point` and `vec`
/usr/bin/dmd failed with exit code 1.
```
I tried to implement a single template:
```d
mixin template sumDiff(T, R){
R opBinary(string op)(T rhs) const
if (op == "+" || op == "-"){
return mixin("R(x " ~ op ~ " rhs.x, y " ~ op ~ "rhs.y, z "
~ op ~ " rhs.z)");
}
}
```
but the same error occurs.
If I don't use the mixin templates and, instead, I overload the
operations into the structures everything works.
```d
struct point{
float x, y, z;
vec opBinary(string op)(point rhs) const
if (op == "-") {
return vec(x - rhs.x, y - rhs.y, z - rhs.z);
}
point opBinary(string op)(vec rhs) const
if (op == "+") {
return point(x + rhs.x, y + rhs.y, z + rhs.z);
}
}
struct vec{
float x, y, z;
}
void main(){
point p1 = {1,2,3}, p2 = {5,6,7};
vec v1 = p1-p2;
vec v2 = {2,-1,0};
point p3 = p1+v2;
}
```
Am I doing something wrong or it is impossible to use mixin
templates like that?
