Hello,
could someone plz clearify what the exact semantics of "put"
are ?
Put works with an appender, but gives me a runtime exception
when using an array.

Best regards,
Oliver

O.K. wrote:
> Hello,
> could someone plz clearify what the exact semantics of "put"
> are ?
> Put works with an appender, but gives me a runtime exception
> when using an array.
> 
> Best regards,
> Oliver

The source code for the standard library comes with the compiler.

If you look in std\array.d, you find this around line 279 (reflowed for
readability):

> void put(T, E)(ref T[] a, E e) {
>     assert(a.length);
>     a[0] = e; a = a[1 .. $];
> }

Good point ! Use the [S/F]o[u]rce !
Thx, Oliver

> O.K. wrote:
> > Hello,
> > could someone plz clearify what the exact semantics of "put"
> > are ?
> > Put works with an appender, but gives me a runtime exception
> > when using an array.
> >
> > Best regards,
> > Oliver
> The source code for the standard library comes with the compiler.
> If you look in std\array.d, you find this around line 279 (reflowed for
> readability):
> > void put(T, E)(ref T[] a, E e) {
> >     assert(a.length);
> >     a[0] = e; a = a[1 .. $];
> > }

Oliver wrote:
>> The source code for the standard library comes with the compiler.
>> If you look in std\array.d, you find this around line 279 (reflowed for
>> readability):
>>> void put(T, E)(ref T[] a, E e) {
>>>     assert(a.length);
>>>     a[0] = e; a = a[1 .. $];
>>> }

Would anybody care to explain what this is used for? I find
the example in array.d rather unhelpful.

Example:
----
void main()
{
    int[] a = [ 1, 2, 3 ];
    int[] b = a;
    a.put(5);
    assert(a == [ 2, 3 ]);
    assert(b == [ 5, 2, 3 ]);
}

You're putting an element in a, but then the first element is moved out of a and the new one shows up in b? Weird. I guess I don't understand what a range is.

Jos

Jos van Uden wrote:
> Oliver wrote:
>>> The source code for the standard library comes with the compiler.
>>> If you look in std\array.d, you find this around line 279 (reflowed for
>>> readability):
>>>> void put(T, E)(ref T[] a, E e) {
>>>>     assert(a.length);
>>>>     a[0] = e; a = a[1 .. $];
>>>> }
> 
> Would anybody care to explain what this is used for? I find the example in array.d rather unhelpful.
> 
> Example:
> ----
> void main()
> {
>     int[] a = [ 1, 2, 3 ];
>     int[] b = a;
>     a.put(5);
>     assert(a == [ 2, 3 ]);
>     assert(b == [ 5, 2, 3 ]);
> }
> 
> You're putting an element in a, but then the first element is moved out of a and the new one shows up in b? Weird. I guess I don't understand what a range is.
> 
> Jos

No; read the code.  Before the put, a and b are pointing to the same
span of memory.  a.put(5) puts the value 5 into the front (first
element) of the array, then advances the array.

However, put can't "see" b, so it doesn't get updated along with a.  The end result is that b = [5,2,3] and a = b[1..3] = [2,3].

Why do it like this?  Here's an example:

void putNumbers(Range)(Range r)
{
    int i = 0;
    while( !r.empty )
    {
        r.put(i);
        ++i;
    }
}

void main()
{
    int[10] ten_numbers;
    putNumbers(ten_numbers);
    assert( ten_numbers = [0,1,2,3,4,5,6,7,8,9] );
}

Note that putNumbers will work with any type that supports the range API, not just arrays.

Daniel Keep wrote:

> No; read the code.  Before the put, a and b are pointing to the same
> span of memory.  a.put(5) puts the value 5 into the front (first
> element) of the array, then advances the array.
> 
> However, put can't "see" b, so it doesn't get updated along with a.  The
> end result is that b = [5,2,3] and a = b[1..3] = [2,3].
> 
> Why do it like this?  Here's an example:
> 
> void putNumbers(Range)(Range r)
> {
>     int i = 0;
>     while( !r.empty )
>     {
>         r.put(i);
>         ++i;
>     }
> }
> 
> void main()
> {
>     int[10] ten_numbers;
>     putNumbers(ten_numbers);
>     assert( ten_numbers = [0,1,2,3,4,5,6,7,8,9] );
> }

I see.

Your example should be in the documentation in my opinion, rather
then the meaningless one that's there now. Something like this
perhaps:

void putNumbers(Range, T)(Range r, T start, T incr) {
    T i = start;
    while( !r.empty )
    {
        r.put(i);
        i += incr;
    }
}

void main() {
   int[10] ten_ints;
   putNumbers!(int[])(ten_ints, 4, 2);
   assert( ten_ints == [4,6,8,10,12,14,16,18,20,22] );
}

Jos