March 13, 2013 Re: One case of array assignments | ||||
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Posted in reply to John Colvin | 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);
)
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March 13, 2013 Re: One case of array assignments | ||||
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Posted in reply to John Colvin | 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.
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March 14, 2013 Re: One case of array assignments | ||||
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Posted in reply to H. S. Teoh | 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 = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to Marco Leise | 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).
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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to Chris Nicholson-Sauls | 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 | ||||
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Posted in reply to monarch_dodra | 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.
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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to John Colvin | 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.
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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to monarch_dodra | 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.
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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to Timon Gehr | 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.
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March 18, 2013 Re: One case of array assignments | ||||
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Posted in reply to monarch_dodra | 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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