Re: Default constructor for structs

[bearophile]

Peter Alexander:
> Since default constructors for structs are not allowed, how do I go 
> about making all the elements of this Matrix struct default to zero? 
> (floats default to nan by default).

This doesn't work, I don't know why:
float[M][N] elements = 0.0;

A bad looking solution:

struct Matrix(int M, int N) {
    float[M][N] elements;
    static Matrix opCall() {
        Matrix m;
        foreach (ref row; m.elements)
            row[] = 0.0;
        return m;
    }
}
void main() {
    auto m = Matrix!(3, 3)();
    assert(m.elements[0][0] == 0);
}


A possible solution avoids going against the language (the default nan value 
for FP values isn't there for show, it's there because it improves your code):

struct Matrix(int M, int N) {
    float[M][N] elements;
    this(float init=0) {
        foreach (ref row; elements)
            row[] = init;
    }
}
void main() {
    auto m = Matrix!(3, 3)(0.0);
    assert(m.elements[0][0] == 0);
}


This doesn't work:

struct Matrix(int M, int N) {
    float[M][N] elements;
    this(float init=0.0) {
        foreach (ref row; elements)
            row[] = init;
    }
}
void main() {
    auto m = Matrix!(3, 3)();
    assert(m.elements[0][0] == 0);
}

Bye,
bearophile