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March 13, 2013
Re: One case of array assignments
On 03/13/2013 10:19 PM, John Colvin wrote:
> On Wednesday, 13 March 2013 at 21:08:30 UTC, Timon Gehr wrote:
>> ...
>>
>> That's clearly a valid way of reasoning, however, it is not the only one.
>>
>> int[3] a = 1;
>> int[3] b = 2;
>> int[3] c = 3;
>>
>> int[3][3] x = [a,b,c];
>
> this would also be valid, as you have fully specified the elements of
> the array. I don't see the conflict?

This was supposed to be a justification for int[3][3] x = [1,2,3]; 
denoting int[3][3] x = [[1,1,1],[2,2,2],[3,3,3]];

I think any one way to define the initialization semantics is arbitrary.

It is not necessary anyway, the language is versatile enough:

import std.stdio : writeln;
import std.algorithm, std.range;

auto array(R)(R r){ // phobos' version still not ctfe-able...
    typeof({foreach(x;r)return x;assert(0);}())[] a;
    foreach(x;r) a~=x;
    return a;
}

auto erep(R)(R r, size_t n){ return r.repeat(n).array; }
auto emap(alias a, R)(R r){ return r.map!a.array; }

auto rows(T)(T[] x,size_t n){ return x.erep(3); }
auto cols(T)(T[] x,size_t n){ return x.emap!(a=>a.erep(3)); }


int[3][3] x = [1,2,3].rows(3);
int[3][3] y = [1,2,3].cols(3);
void main(){
    assert(x[]==[[1, 2, 3], [1, 2, 3], [1, 2, 3]]);
    assert(y[]==[[1, 1, 1], [2, 2, 2], [3, 3, 3]]);
}

(using one of bearophiles turned-down enhancement requests:
  int[$][$] x = [1,2,3].rows(3);
  int[$][$] y = [1,2,3].cols(3);
)
March 13, 2013
Re: One case of array assignments
On 03/13/2013 10:40 PM, John Colvin wrote:
> On Wednesday, 13 March 2013 at 21:33:47 UTC, H. S. Teoh wrote:
>> ...
>>
>> Why is it bad to have to explicitly list the elements for static
>> initialization?
>>
>>
>> T
>
> I would be great if we could get rid of post-fix array declarations for
> good, but I'm not sure how realistic that is.
>
>
> It's bad to have to explicitly list them because there could be
> hundreds, thousands or even millions of elements.

But we have full compile-time function evaluation available, enabling 
initializer compression in much more involved ways.
March 14, 2013
Re: One case of array assignments
Am Wed, 13 Mar 2013 14:31:42 -0700
schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:

> Why is it bad to have to explicitly list the elements for static
> initialization?

Because of:

struct CompressionData
{
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0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0];
}

-- 
Marco
March 18, 2013
Re: One case of array assignments
On Thursday, 14 March 2013 at 01:34:02 UTC, Marco Leise wrote:
> Am Wed, 13 Mar 2013 14:31:42 -0700
> schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:
>
>> Why is it bad to have to explicitly list the elements for 
>> static
>> initialization?
>
> Because of:
>
> struct CompressionData
> {
> 	ubyte[4096] x =
> [0,0,0 /* ...ad nauseum... */ ,0,0];
> }

struct CompressionData
{
    ubyte[4096] x; // note this is already [0...0] thanks
                   // to default init... but still:

    this ()
    {
        x[] = 0;
    }
}


--- Or even: ---

import std.range;

struct CompressionData
{
    ubyte[4096] x = repeat( 0 )[ 0 .. 4096 ];
}

Assuming repeat()[] is CTFE-able (didn't test).
March 18, 2013
Re: One case of array assignments
On Monday, 18 March 2013 at 21:35:43 UTC, Chris Nicholson-Sauls 
wrote:
> On Thursday, 14 March 2013 at 01:34:02 UTC, Marco Leise wrote:
>> Am Wed, 13 Mar 2013 14:31:42 -0700
>> schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:
>>
>>> Why is it bad to have to explicitly list the elements for 
>>> static
>>> initialization?
>>
>> Because of:
>>
>> struct CompressionData
>> {
>> 	ubyte[4096] x =
>> [0,0,0 /* ...ad nauseum... */ ,0,0];
>> }
>
> struct CompressionData
> {
>     ubyte[4096] x; // note this is already [0...0] thanks
>                    // to default init... but still:
>
>     this ()
>     {
>         x[] = 0;
>     }
> }

The downside here is that this requires run-time initialization.

> --- Or even: ---
>
> import std.range;
>
> struct CompressionData
> {
>     ubyte[4096] x = repeat( 0 )[ 0 .. 4096 ];
> }
>
> Assuming repeat()[] is CTFE-able (didn't test).

Better, but that doesn't compime, because "repeat( 0 )[ 0 .. 4096 
]" is not an actual array, but a complex type. And of type int. 
The correct code would be:

ubyte[4096] x = repeat( cast(ubyte)0 )[ 0 .. 4096 ].array();

This can be used as-is inside normal code. Hwoever, array is not 
CTFE-able, so it can't work to define a struct T.init value.
March 18, 2013
Re: One case of array assignments
On Monday, 18 March 2013 at 21:45:55 UTC, monarch_dodra wrote:
>
> The downside here is that this requires run-time initialization.
>

Is the normal syntax compile time actually? Incorrect dimensions 
for initialisation of a static array is a runtime error, so i 
suspect it's not.
March 18, 2013
Re: One case of array assignments
On Monday, 18 March 2013 at 21:50:30 UTC, John Colvin wrote:
> On Monday, 18 March 2013 at 21:45:55 UTC, monarch_dodra wrote:
>>
>> The downside here is that this requires run-time 
>> initialization.
>>
>
> Is the normal syntax compile time actually? Incorrect 
> dimensions for initialisation of a static array is a runtime 
> error, so i suspect it's not.

At worse, it is a CTFE-able syntax, because default value of all 
fields of a struct MUST be evaluated during compile, to evaluate 
T.init.
March 18, 2013
Re: One case of array assignments
On 03/18/2013 10:45 PM, monarch_dodra wrote:
> ...
>
> ubyte[4096] x = repeat( cast(ubyte)0 )[ 0 .. 4096 ].array();
>
> This can be used as-is inside normal code. Hwoever, array is not
> CTFE-able, so it can't work to define a struct T.init value.

Which is annoying and should be fixed.
March 18, 2013
Re: One case of array assignments
On Monday, 18 March 2013 at 22:33:17 UTC, Timon Gehr wrote:
> On 03/18/2013 10:45 PM, monarch_dodra wrote:
>> ...
>>
>> ubyte[4096] x = repeat( cast(ubyte)0 )[ 0 .. 4096 ].array();
>>
>> This can be used as-is inside normal code. Hwoever, array is 
>> not
>> CTFE-able, so it can't work to define a struct T.init value.
>
> Which is annoying and should be fixed.

Making array work with CTFE is a no-go, as array's job is to 
run-time allocate a new array.

The syntax "T[N] = R.array" actually first transforms the range 
into a (dynamic) array, and then copies it into the static array. 
It is wasteful, but works. It is completely un-doable at compile 
time though.

Now, if we had "staticArray(R, Sizes)(R)" transforms a range into 
an array whose size is know at compile time, then that's another 
story. It'd be more efficient at run-time, and CTFE-able

1) Do we want such a weird and specific function? Or is that just 
premature optimization? I mean, is there a real need?
2) Given CTFE's bug of "mutation implies duplication", I'm unsure 
providing such a function would be wise.
March 18, 2013
Re: One case of array assignments
On 03/18/2013 11:52 PM, monarch_dodra wrote:
> On Monday, 18 March 2013 at 22:33:17 UTC, Timon Gehr wrote:
>> On 03/18/2013 10:45 PM, monarch_dodra wrote:
>>> ...
>>>
>>> ubyte[4096] x = repeat( cast(ubyte)0 )[ 0 .. 4096 ].array();
>>>
>>> This can be used as-is inside normal code. Hwoever, array is not
>>> CTFE-able, so it can't work to define a struct T.init value.
>>
>> Which is annoying and should be fixed.
>
> Making array work with CTFE is a no-go, as array's job is to run-time
> allocate a new array.
>

Uh. Its job is to collect a range into an array. Implementation details 
are irrelevant.

> The syntax "T[N] = R.array" actually first transforms the range into a
> (dynamic) array, and then copies it into the static array. It is
> wasteful, but works. It is completely un-doable at compile time though.
>

You mean impossible? Of course it is possible.

> Now, if we had "staticArray(R, Sizes)(R)" transforms a range into an
> array whose size is know at compile time, then that's another story.
> It'd be more efficient at run-time, and CTFE-able
>

Sizes should go first.

> 1) Do we want such a weird and specific function? Or is that just
> premature optimization? I mean, is there a real need?

Use 'copy'.

> 2) Given CTFE's bug of "mutation implies duplication", I'm unsure
> providing such a function would be wise.

DMD bug, not CTFE bug.
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