I'm new to D2, so please.. :)

The spec on Array Operations, http://www.digitalmars.com/d/2./arrays.html says:
"""A vector operation is indicated by the slice operator appearing as the lvalue of an =, +=, -=, *=, /=, %=, ^=, &= or |= operator."""

The following tests works fine as I expected:


	{
		double[3] a = [1,1,1];
		double[3] b;
		b[] = a[] + 3;
		assert(a == [1,1,1]);
		assert(b == [4,4,4]);
	}
	
	{
		double[3] a = [1,1,1];
		auto b = a;
		b[] = a[] + 3;
		assert(a == [1,1,1]);
		assert(b == [4,4,4]);
	}

But from here on I'm having problems...

	{
		double[] a = [1,1,1];
		double[] b;
		b[] = a[] + 3;
		assert(a == [1,1,1]);
		assert(b == [4,4,4]); // fails as b.length == 0.. Should the compiler say something?
	}
	
	{
		double[] a = [1,1,1];
		double[] b;
		b.length = a.length;
		b[] = a[] + 3;
		assert(a == [1,1,1]);
		assert(b == [4,4,4]); // Now it's fine
	}
	
	{
		double[3] a = [1,1,1];
		double[3] b = a[] + 3; // works although lvalue isn't a slice. Static arrays? Because it's an initial value?
		assert(a == [1,1,1]);
		assert(b == [4,4,4]);
	}
	
	{
		double[3] a = [1,1,1];
		auto b = a;
		b = a[] + 3; // And so does this.. Something to do with static arrays?
		assert(a == [1,1,1]);
		assert(b == [4,4,4]);
	}
	
	{ // Like the previous example, but with dynamic arrays..
		double[] a = [1,1,1];
		auto b = a;
		assert(a is b);
		b = a[] + 3;
		assert(a == [1,1,1]);
		//writeln(b); // access violation. Because of dynamic arrays?
	}	

	{ // Like above, but using slicing like the spec says.. Works fine
		double[] a = [1,1,1];
		auto b = a;
		assert(a is b);
		writeln(typeof(b).stringof); // double[]
		b[] = a[] + 3;
		assert(a == [4,4,4]); // a also changed. I expected this
		assert(b == [4,4,4]);
	}
	
	{
		double[3] a = [1,1,1];
		auto b = a[] + 3; // What happens here?
		writeln(typeof(b).stringof); // double[]
		assert(b.length == 3);
		assert(b.capacity == 0);
		//writeln(b); // access violation
	}
	
	{ // Same as above?
		double[3] a = [1,1,1];
		//writeln(a[] + 3); // access violation
	}
	

Am 07.08.2010 14:10, schrieb simendsjo:
> I'm new to D2, so please.. :)
>
> The spec on Array Operations,
> http://www.digitalmars.com/d/2./arrays.html says:
> """A vector operation is indicated by the slice operator appearing as
> the lvalue of an =, +=, -=, *=, /=, %=, ^=, &= or |= operator."""
>
> The following tests works fine as I expected:
>
>
> {
> double[3] a = [1,1,1];
> double[3] b;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> {
> double[3] a = [1,1,1];
> auto b = a;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> But from here on I'm having problems...
>
> {
> double[] a = [1,1,1];
> double[] b;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]); // fails as b.length == 0.. Should the compiler
> say something?
> }
>
> {
> double[] a = [1,1,1];
> double[] b;
> b.length = a.length;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]); // Now it's fine
> }
>
> {
> double[3] a = [1,1,1];
> double[3] b = a[] + 3; // works although lvalue isn't a slice. Static
> arrays? Because it's an initial value?
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> {
> double[3] a = [1,1,1];
> auto b = a;
> b = a[] + 3; // And so does this.. Something to do with static arrays?
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> { // Like the previous example, but with dynamic arrays..
> double[] a = [1,1,1];
> auto b = a;
> assert(a is b);
> b = a[] + 3;
> assert(a == [1,1,1]);
> //writeln(b); // access violation. Because of dynamic arrays?
> }
>
> { // Like above, but using slicing like the spec says.. Works fine
> double[] a = [1,1,1];
> auto b = a;
> assert(a is b);
> writeln(typeof(b).stringof); // double[]
> b[] = a[] + 3;
> assert(a == [4,4,4]); // a also changed. I expected this
> assert(b == [4,4,4]);
> }
>
> {
> double[3] a = [1,1,1];
> auto b = a[] + 3; // What happens here?
> writeln(typeof(b).stringof); // double[]
> assert(b.length == 3);
> assert(b.capacity == 0);
> //writeln(b); // access violation
> }
>
> { // Same as above?
> double[3] a = [1,1,1];
> //writeln(a[] + 3); // access violation
> }
>
Hi,
I don't the answer to all of your problems but what I can say you is:
* D-Arrays are references to structs which point to the data
* An arrayvariable on the left-hand-side of an assignment sets the reference of this variable. (no copy!)
* An array slice is mostly the same as the array variable itself but if it's on the left-hand-side of an assignment, the data is copied from the right-hand-side.

So for example your third example can't work because b is null and so there's no place you can copy the data to.

Hey, here Mafi again,
I thought about your snippets and here's what I have.

Am 07.08.2010 14:10, schrieb simendsjo:
> {
> double[3] a = [1,1,1];
> double[3] b;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> {
> double[3] a = [1,1,1];
> auto b = a;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
>
> But from here on I'm having problems...
>
> {
> double[] a = [1,1,1];
> double[] b;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]); // fails as b.length == 0.. Should the compiler say something?
> }
As I said in my first post b is null. Now the third line tries to _copy_ the result to b which is impossible. About your question:
that the compiler complains would be difficult but in my opinion it should result in an runtime error.
>
> {
> double[] a = [1,1,1];
> double[] b;
> b.length = a.length;
> b[] = a[] + 3;
> assert(a == [1,1,1]);
> assert(b == [4,4,4]); // Now it's fine
> }
With setting b's length you (re)allocate(1) memory for the array so now there's place to copy to.

> {
> double[3] a = [1,1,1];
> double[3] b = a[] + 3; // works although lvalue isn't a slice. Static
> arrays? Because it's an initial value?
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
You simply intialize the fixed-size array with a dynamic one. I'm not sure but I think the data is copied out of the dynamic temporary array to b.
> {
> double[3] a = [1,1,1];
> auto b = a;
> b = a[] + 3; // And so does this.. Something to do with static arrays?
> assert(a == [1,1,1]);
> assert(b == [4,4,4]);
> }
In the second line you initialize to a and then do the same as above.
Note: In D fixed-size arrays are value types.
> { // Like the previous example, but with dynamic arrays..
> double[] a = [1,1,1];
> auto b = a;
> assert(a is b);
> b = a[] + 3;
> assert(a == [1,1,1]);
> //writeln(b); // access violation. Because of dynamic arrays?
> }
I have no idea. Maybe the array generated by the vector addition is kind of temporary and you have to copy. But it could also be a bug.
Vector-operations are still quite buggy.
> { // Like above, but using slicing like the spec says.. Works fine
> double[] a = [1,1,1];
> auto b = a;
> assert(a is b);
> writeln(typeof(b).stringof); // double[]
> b[] = a[] + 3;
> assert(a == [4,4,4]); // a also changed. I expected this
> assert(b == [4,4,4]);
> }
Now you are copying to b(which references the same struct as a).
> {
> double[3] a = [1,1,1];
> auto b = a[] + 3; // What happens here?
> writeln(typeof(b).stringof); // double[]
> assert(b.length == 3);
> assert(b.capacity == 0);
> //writeln(b); // access violation
> }
It's the same as to steps before this(my  english isn't ver good ;))
> { // Same as above?
I think it is.
> double[3] a = [1,1,1];
> //writeln(a[] + 3); // access violation
> }
>
(1)It's normally for reallocation when you need more space.

Mafi wrote:
> Hey, here Mafi again,
> I thought about your snippets and here's what I have.
> 
> Am 07.08.2010 14:10, schrieb simendsjo:

>> { // Like the previous example, but with dynamic arrays..
>> double[] a = [1,1,1];
>> auto b = a;
>> assert(a is b);
>> b = a[] + 3;
>> assert(a == [1,1,1]);
>> //writeln(b); // access violation. Because of dynamic arrays?
>> }
> I have no idea. Maybe the array generated by the vector addition is kind of temporary and you have to copy. But it could also be a bug.
> Vector-operations are still quite buggy.

That is bug 4578, which has been fixed, and will be in the next compiler release.

On 07.08.2010 14:10, simendsjo wrote:
> I'm new to D2, so please.. :)
>
(...)

Thanks for all answers. Seems array operations is a bit buggy, so I'll rather look more into them at a later date.