Reordered class fields?

[bearophile]

D classes are free to reorder their fields, so maybe Bar1 should 
reorder its fields as Bar3, to save 4 bytes for each instance on 
32 bit systems:

class Bar1 {
    void Hello() {}
    float f;
    double d;
}
class Bar2 {
    void Hello() {}
    align(4) float f;
    align(4) double d;
}
class Bar3 {
    void Hello() {}
    double d;
    float f;
}
void main() {
    pragma(msg, __traits(classInstanceSize, Bar1)); // 24
    pragma(msg, __traits(classInstanceSize, Bar2)); // 20
    pragma(msg, __traits(classInstanceSize, Bar3)); // 20
}



This benchmark shows that if you allocate the class instances on 
the heap one at a time the total amount of memory used is the 
same for the various Bar (maybe because of the GC), so that 
optimization is useful for emplace() only and similar in-place 
allocations:


class Bar1 {
    void Hello() {}
    float f;
    double d;
}
class Bar2 {
    void Hello() {}
    align(4) float f;
    align(4) double d;
}
class Bar3 {
    void Hello() {}
    double d;
    float f;
}
int main() {
    pragma(msg, __traits(classInstanceSize, Bar1)); // 24
    pragma(msg, __traits(classInstanceSize, Bar2)); // 20
    pragma(msg, __traits(classInstanceSize, Bar3)); // 20
    //--------------
    //auto arr = new Bar1[1_000_000]; // 38.2 MB
    //auto arr = new Bar2[1_000_000]; // 38.2 MB
    auto arr = new Bar3[1_000_000]; // 38.2  MB
    foreach (ref a; arr)
        a = new typeof(arr[0])();
    int count;
    foreach (i; 0 .. 500_000_000) count++;
    return count;
}


So is such class field reordering worth an enhancement request in 
Bugzilla?

Bye,
bearophile