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).

struct Matrix(int M, int N)
{
	float[M][N] elements;
}

Matrix(3, 3) m;
assert(m[0][0] == 0);

?

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

On 7/08/10 3:44 PM, bearophile wrote:
> Peter Alexander:
> <snip>
>
> Bye,
> bearophile

Thanks for your detailed reply.

However, I'm not particularly satisfied with any of those :(

I have already gone with the single parameter init constructor in my code until I find something better, but really, I just want the matrix to be default initialised to zeroes without having to explicitly specify it in client code.

Initialising to NaNs is highly unintuitive (especially since ints auto-initialise to 0...) and this has already caused me unnecessary grief. I understand the reasoning, and I might agree with it if it wasn't forced on you...

Hi, I'm a newbie, hope the attached example works for you.

Peter Alexander wrote:
> 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).
> 
> struct Matrix(int M, int N)
> {
>     float[M][N] elements;
> }
> 
> Matrix(3, 3) m;
> assert(m[0][0] == 0);
> 
> ?

oops :p correction:
in template Zero
const float[M][N] ==> const T[M][N]

rouge wrote:
> Hi, I'm a newbie, hope the attached example works for you.
> 
> Peter Alexander wrote:
>> 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).
>>
>> struct Matrix(int M, int N)
>> {
>>     float[M][N] elements;
>> }
>>
>> Matrix(3, 3) m;
>> assert(m[0][0] == 0);
>>
>> ?