Hello,

I am a learning D, and so far I am enjoying it. However, since I have a few doubts I cannot clear just by reading the available documentation, I registered in this list, so please bear with me if my questions sound a bit dumb.

So my first doubt is this:

What is the proper D syntax to initialize a static array with consecutive integers starting with 1?

I know I could simply use "for" like in C, but while reading the web documentation on arrays, I noticed the vector notation. According to the documentation, this code:
T[] a, b;
...
a[] = b[] + 4;

is equivalent to this code:
T[] a, b;
...
for (size_t i = 0; i < a.length; i++) a[i] = b[i] + 4;

Now, suppose I declare a static array:
int[100] myarray;

What would be the substitution in vector notation for this code?
for (int i =0; i < myarray.length; i++) myarray[i] = i +1;

I have tried these, and neither seems to work as expected (they simply assign 0+1 to every element):
myarray[] += 1;
myarray[] = myarray[] + 1;

I also tried using the array as an aggregate in a foreach statement:
foreach(int i, int j, myarray) j = i + 1;

However, it does not work this way because apparently the j variable seems to work only for reading, not for assigning. I wonder why this limitation in behavior, if according to the documentation:

"If there are two variables declared, the first is said to be the index and the second is said to be the value [set to the elements of the array, one by one]"

So if j refers to the value, the intuitive thing IMHO would be assigning to each element when one assigns to j. Oherwise one would have to do something redundant like this:
foreach(int i, int j, myarray) myarray[i] = j = i + 1;

Or maybe this (which renders j useless altogether)
foreach(int i, int j, myarray) myarray[i] = i + 1;

Or even something like this (which works, but misses the advantage of using the array as an aggregate):
foreach(int i; 0..myarray.length) myarray[i] = i + 1;

Or I am missing something?
Either way, please advice the recommended D way.

Regards, Hugo

On 03/08/2012 06:02 PM, Hugo Florentino wrote:

> What is the proper D syntax to initialize a static array with
> consecutive integers starting with 1?

One of many ways:

int[N] makeArray(size_t N)()
{
    int[N] result;

    foreach (int i, ref element; result) {
        element = i;
    }

    return result;
}

void main()
{
    assert(makeArray!4() == [ 0, 1, 2, 3 ]);
}

> I know I could simply use "for" like in C, but while reading the web
> documentation on arrays, I noticed the vector notation. According to the
> documentation, this code:
> T[] a, b;
> ...
> a[] = b[] + 4;
>
> is equivalent to this code:
> T[] a, b;
> ...
> for (size_t i = 0; i < a.length; i++) a[i] = b[i] + 4;

It should be possible to use a special type and keep state to achieve it with the arraywise syntax but this task is natural for that syntax.

> I also tried using the array as an aggregate in a foreach statement:
> foreach(int i, int j, myarray) j = i + 1;
>
> However, it does not work this way because apparently the j variable
> seems to work only for reading, not for assigning. I wonder why this
> limitation in behavior, if according to the documentation:
>
> "If there are two variables declared, the first is said to be the index
> and the second is said to be the value [set to the elements of the
> array, one by one]"
>
> So if j refers to the value,

That's the problem. j does not refer to the element, it is a copy of it. You must use the 'ref' keyword as in the code that I have shown above.

> Either way, please advice the recommended D way.

There are many ways of initializing a fixed-length array with consecutive integers. Here is another one:

import std.algorithm;
import std.range;

void main()
{
    int[4] array = array(iota(4));
    assert(array == [ 0, 1, 2, 3 ]);
}

>
> Regards, Hugo

Ali

P.S. There is also the D.learn newsgroup where such threads are very welcome at. :)