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digitalmars.D.learn - typeof([2,2]) !=? int[2]

reply "Zhenya" <zheny list.ru> writes:
Hi!
Explain me please,what's wrong with this code:

struct NDimensionalArray(T,alias size)
	if(is(typeof(size) _ == int[n],int n) &&
	   n > 0)
{
	static if(n > 1)
		NDimensionalArray!(T,n - 1,size[1..$]) m_array[size[0]];
	else
		T m_array[size[0]];
	alias m_array this;
}

void main()
{
	NDimensionalArray!(int,[2,2]) array;
	array[0][1] = 1;
}

It fails with message:
Error: template instance NDimensionalArray!(int, [2, 2]) 
NDimensionalArray!(int, [2, 2]) does not match template 
declaration NDimensionalArray(T, alias size) if (is(typeof(size) 
_ == int[n],int n) && n > 0)
on dmd git-head.
Mar 08 2013
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
This is an answer to just your title question.

A lot of time ago typeof([2,2]) was int[2]. This was efficient, 
but in most cases this was a source of troubles and bugs. So now 
a [2,2] is a heap-allocated dynamic array of type int[]. Some 
persons have askes for a fixed-sized array litera, like s[2,2] 
but nothing has happened on this so far.

Bye,
bearophile
Mar 08 2013
parent reply "Zhenya" <zheny list.ru> writes:
On Friday, 8 March 2013 at 22:59:40 UTC, bearophile wrote:

 This is an answer to just your title question.

 A lot of time ago typeof([2,2]) was int[2]. This was efficient, 
 but in most cases this was a source of troubles and bugs. So 
 now a [2,2] is a heap-allocated dynamic array of type int[]. 
 Some persons have askes for a fixed-sized array litera, like 
 s[2,2] but nothing has happened on this so far.

 Bye,
 bearophile


Thank you very much.
Mar 08 2013
next sibling parent "Zhenya" <zheny list.ru> writes:
On Friday, 8 March 2013 at 23:03:47 UTC, Zhenya wrote:

 On Friday, 8 March 2013 at 22:59:40 UTC, bearophile wrote:

 This is an answer to just your title question.

 A lot of time ago typeof([2,2]) was int[2]. This was 
 efficient, but in most cases this was a source of troubles and 
 bugs. So now a [2,2] is a heap-allocated dynamic array of type 
 int[]. Some persons have askes for a fixed-sized array litera, 
 like s[2,2] but nothing has happened on this so far.

 Bye,
 bearophile


 Thank you very much.


Although it's a bit strange,since we can always pass heap 
allocated array by
using new.
Mar 08 2013
prev sibling parent reply "cal" <callumenator gmail.com> writes:
On Friday, 8 March 2013 at 23:03:47 UTC, Zhenya wrote:

Your constraint could be:

if(is(typeof(size) _ == int[]) && size.length > 0)

Also it looks like you are passing 1 too many template args?

static if(n > 1)
   NDimensionalArray!(T,n - 1,size[1..$]) m_array[size[0]];
                              ^^
Mar 08 2013
parent reply "Zhenya" <zheny list.ru> writes:
On Friday, 8 March 2013 at 23:09:07 UTC, cal wrote:

 On Friday, 8 March 2013 at 23:03:47 UTC, Zhenya wrote:

 Your constraint could be:

 if(is(typeof(size) _ == int[]) && size.length > 0)

 Also it looks like you are passing 1 too many template args?

 static if(n > 1)
   NDimensionalArray!(T,n - 1,size[1..$]) m_array[size[0]];
                              ^^


Yes,it's a typo.But it seems to be ugly pass dynamically 
allocated array through
a template parameter,because it's size should be compile-time 
constant.
Mar 08 2013
parent reply "cal" <callumenator gmail.com> writes:
On Friday, 8 March 2013 at 23:15:30 UTC, Zhenya wrote:

 Yes,it's a typo.But it seems to be ugly pass dynamically 
 allocated array through
 a template parameter,because it's size should be compile-time 
 constant.


Its size is a compile-time constant because it is an array 
literal. The size is known inside the constraint.
Mar 08 2013
parent "Zhenya" <zheny list.ru> writes:
On Friday, 8 March 2013 at 23:18:52 UTC, cal wrote:

 On Friday, 8 March 2013 at 23:15:30 UTC, Zhenya wrote:

 Yes,it's a typo.But it seems to be ugly pass dynamically 
 allocated array through
 a template parameter,because it's size should be compile-time 
 constant.


 Its size is a compile-time constant because it is an array 
 literal. The size is known inside the constraint.


Yes,really.
I thought that dynamic allocation is runtime operation
Mar 08 2013