• Peter Alexander (10/10) Aug 07 2010 Since default constructors for structs are not allowed, how do I go
• bearophile (43/46) Aug 07 2010 This doesn't work, I don't know why:
• Peter Alexander (11/15) Aug 07 2010 Thanks for your detailed reply.
• rouge (2/15) Aug 07 2010
• rouge (4/20) Aug 07 2010 oops :p correction:

Peter Alexander <peter.alexander.au gmail.com> writes:

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);

?

bearophile <bearophileHUGS lycos.com> writes:

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

Peter Alexander <peter.alexander.au gmail.com> writes:

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...

rouge <rouge gmail.com> writes:

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);
 
 ?

rouge <rouge gmail.com> writes:

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);

 ?