Is this a good way to get the depth of an array?

int getArrayDepth(T)(ref T array)
{
static if( is(T A:A[]) )
{
A arr;
return 1 + getArrayDepth(arr);
}
else
{
return 0;
}
return -1;
}

Hello Saaa,

> Is this a good way to get the depth of an array?
> 
> int getArrayDepth(T)(ref T array)
> {
> static if( is(T A:A[]) )
> {
> A arr;
> return 1 + getArrayDepth(arr);
> }
> else
> {
> return 0;
> }
> return -1;
> }

I just posted this today

http://www.dsource.org/projects/scrapple/browser/trunk/Serial/utill.d

On Thu, Jun 11, 2009 at 9:15 PM, Saaa<empty@needmail.com> wrote:
> Is this a good way to get the depth of an array?
>
> int getArrayDepth(T)(ref T array)
> {
> static if( is(T A:A[]) )
> {
> A arr;
> return 1 + getArrayDepth(arr);
> }
> else
> {
> return 0;
> }
> return -1;
> }

It's kind of the right idea, but.. it's also kind of weird.

template ArrayDepth(T: T[]) { const ArrayDepth = 1 + ArrayDepth!(T); }
template ArrayDepth(T)       { const ArrayDepth = 0; }

This lets you get the depth of any array _type_, like
ArrayDepth!(int[][]) gives 2.

>
> It's kind of the right idea, but.. it's also kind of weird.
>
> template ArrayDepth(T: T[]) { const ArrayDepth = 1 + ArrayDepth!(T); }
> template ArrayDepth(T)       { const ArrayDepth = 0; }
>
> This lets you get the depth of any array _type_, like
> ArrayDepth!(int[][]) gives 2.

Ah , that's how you make it do at compile time, using const.

BCS also did it a bit like me (one template that is) I just didn't know you
could also just pass the type :D
Any advantage to using two?

He also does :  is( T B ==B[])  iso  is( T B:B[] )
Any significant difference there?

Also, what's the advantage of explicitly defining it as a template?

On Thu, Jun 11, 2009 at 11:02 PM, Saaa<empty@needmail.com> wrote:
> Any advantage to using two?

I just tend to prefer template specialization when doing type pattern matching.  It works out better than is() in some cases.

> He also does :  is( T B ==B[])  iso  is( T B:B[] )
> Any significant difference there?

I'm.. not sure, in this case anyway.  Normally == does strict type comparison while : does implicit type conversion, but in this case, is() is being (ab)used to pick apart a type rather than test one.  I think it'll always return 'true' in either case if T is an array, so I don't think there's a functional difference.

> Also, what's the advantage of explicitly defining it as a template?

As opposed to what, implicitly defining it as a template?  This question doesn't really make sense.

>> Any advantage to using two?
>
> I just tend to prefer template specialization when doing type pattern matching.  It works out better than is() in some cases.
Looks very Haskell like :)
>
>> He also does :  is( T B ==B[])  iso  is( T B:B[] )
>> Any significant difference there?
>
> I'm.. not sure, in this case anyway.  Normally == does strict type comparison while : does implicit type conversion, but in this case, is() is being (ab)used to pick apart a type rather than test one.  I think it'll always return 'true' in either case if T is an array, so I don't think there's a functional difference.

Implicit convertion sounds a bit dangerous, might start using == instead

>
>> Also, what's the advantage of explicitly defining it as a template?
>
> As opposed to what, implicitly defining it as a template?  This question doesn't really make sense.

I mean, I was using a function template.

> template ArrayDepth(T: T[]) { const ArrayDepth = 1 + ArrayDepth!(T); }
> template ArrayDepth(T)       { const ArrayDepth = 0; }

The code looks a bit strange to me:
ArrayDepth is both a (const) value and template name and where is the return
value ?

> It's kind of the right idea, but.. it's also kind of weird.
>
> template ArrayDepth(T: T[]) { const ArrayDepth = 1 + ArrayDepth!(T); }
> template ArrayDepth(T)       { const ArrayDepth = 0; }
>
> This lets you get the depth of any array _type_, like
> ArrayDepth!(int[][]) gives 2.

Although I don't fully understand your code, I think I modified it correctly to get the base type of an array :)

template BaseType(T: T[]) { const BaseType = BaseType!(T); }
template BaseType(T) {const BaseType = T; }

>
> template BaseType(T: T[]) { const BaseType = BaseType!(T); }
> template BaseType(T) {const BaseType = T; }

..
else static if( std2.traits.isNumeric!( BaseType!(T) ) )
{
..

ddata\ddata.d(192): template instance isNumeric!(int) does not match any
template declaration
ddata\ddata.d(192): Error: expression isNumeric!(int) is not constant or
does not evaluate to a bool

What am I doing wrong?

On Fri, Jun 12, 2009 at 12:04 AM, Saaa<empty@needmail.com> wrote:
>>
>> template BaseType(T: T[]) { const BaseType = BaseType!(T); }
>> template BaseType(T) {const BaseType = T; }
>
> ..
> else static if( std2.traits.isNumeric!( BaseType!(T) ) )
> {
> ..
>
> ddata\ddata.d(192): template instance isNumeric!(int) does not match any
> template declaration
> ddata\ddata.d(192): Error: expression isNumeric!(int) is not constant or
> does not evaluate to a bool
>
> What am I doing wrong?

Your template.  Types are not values, you cannot declare a constant that is a type.  You have to use alias instead:

template BaseType(T: T[]) { alias BaseType!(T) BaseType; }
template BaseType(T) { alias T BaseType; }