www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - MultiDimensional Associative Arrays

reply Trevor Parscal <Trevor_member pathlink.com> writes:
MultiDimensional Associative Arrays

Perhaps this is possible, and I don't know how to use it, but maybe it's not
supported.

if i want an array of class foo indexed by char[] and than by int..

foo[char[]][int] myarray;

so a structure looks like this...

myarray
{
"one"
{
1
2
3
}
"two"
{
1
2
}
"three"
{
1
}
"four"
{
1
2
3
4
}
}

i would access like this...

myfoo = myarray["one"][1];

and check to see if a member exists like this?

foo[int]* name;
name = ("one" in myarray);
if(name != null)
{
foo[int]* value;
value = (1 in name);
if(value != null)
{
// value is a pointer to myarray["one"][1]
}
}

Am I way off base? This doesn't compile right, but it made sense when i wrote
it... The compiler thinks I am trying to "implicitly cast name of type char to
int"

Any and all help would be GREATLY appriciated.

Thanks,
Trevor Parscal
www.trevorparscal.com
trevorparscal hotmail.com
May 21 2005
next sibling parent reply Hasan Aljudy <hasan.aljudy gmail.com> writes:
Trevor Parscal wrote:
 MultiDimensional Associative Arrays
 
 Perhaps this is possible, and I don't know how to use it, but maybe it's not
 supported.
 
 if i want an array of class foo indexed by char[] and than by int..
 
 foo[char[]][int] myarray;
 
 so a structure looks like this...
 
 myarray
 {
 "one"
 {
 1
 2
 3
 }
 "two"
 {
 1
 2
 }
 "three"
 {
 1
 }
 "four"
 {
 1
 2
 3
 4
 }
 }
 
 i would access like this...
 
 myfoo = myarray["one"][1];
 
 and check to see if a member exists like this?
 
 foo[int]* name;
 name = ("one" in myarray);
 if(name != null)
 {
 foo[int]* value;
 value = (1 in name);
 if(value != null)
 {
 // value is a pointer to myarray["one"][1]
 }
 }
 
 Am I way off base? This doesn't compile right, but it made sense when i wrote
 it... The compiler thinks I am trying to "implicitly cast name of type char to
 int"
 
 Any and all help would be GREATLY appriciated.
 
 Thanks,
 Trevor Parscal
 www.trevorparscal.com
 trevorparscal hotmail.com

I read somewhere here that you have to reverse them when you access them myfoo = myarray[1]["one"]; not sure why, I guess in D, arrays read backwards (relative to C).
May 21 2005
next sibling parent Trevor Parscal <Trevor_member pathlink.com> writes:
myfoo = myarray[1]["one"];

not sure why, I guess in D, arrays read backwards (relative to C).

Yes, that was it! thanks for the help... Trevor Parscal www.trevorparscal.com trevorparscal hotmail.com
May 21 2005
prev sibling parent reply Burton Radons <burton-radons smocky.com> writes:
Hasan Aljudy wrote:
 I read somewhere here that you have to reverse them when you access them
 
 myfoo = myarray[1]["one"];
 
 not sure why, I guess in D, arrays read backwards (relative to C).

There should be a justification somewhere, because this WAS a design change, and there is a reason for it. Here's what I wrote right before the change was adopted when it still worked as in C: I'm also very wary of how layers are taken off of types. On the one hand you have: int [] *foo; // Pointer to an array of int. int [] c = *foo; int [] e = foo [0]; On the other hand you have: char [int] [] bar; // Associative array using int as key and char array as value. char [] d = foo [0]; IOW, the unwrapping goes either right-to-left or left-to-right depending upon what kind of wrapping type is being taken off - or something like that, as the whole thing really makes no sense to me. I would prefer right-to-left consistently, as the latter isn't intuitive: alias char [] string; string [int] bar; // Identical to the first definition of bar. Madness! This wasn't so important with C; arrays weren't useful [edit: and it kind of made sense because declaration equaled usage]. But in D this is really ugly. Consistency please. Modern day edit: I consider this to be a design flaw in C running all the way back to its genesis. Types should be on the right: string : [] char; or better yet: string : array of (char);
May 21 2005
parent reply "Unknown W. Brackets" <unknown simplemachines.org> writes:
I'm not sure that's right.

int[]* is:

A pointer to...
An array of...
ints.

char[int][] is:

An array of...
An array indexed by int, of...
chars.

If I compile this:

	char[int][] tester;
	tester.length = 1;
	char[] test2 = tester[0];

I get:
	cannot implicitly convert expression (tester[0]) of type char[int] to 
char[]

Which seems to support my understanding.  See my other post in this 
thread for more information.

-[Unknown]


 
 There should be a justification somewhere, because this WAS a design 
 change, and there is a reason for it.  Here's what I wrote right before 
 the change was adopted when it still worked as in C:
 
 I'm also very wary of how layers are taken off of types.  On the one 
 hand you have:
 
     int [] *foo; // Pointer to an array of int.
     int [] c = *foo;
     int [] e = foo [0];
 
 On the other hand you have:
 
     char [int] [] bar; // Associative array using int as key and char 
 array as value.
     char [] d = foo [0];
 
 IOW, the unwrapping goes either right-to-left or left-to-right depending 
 upon what kind of wrapping type is being taken off - or something like 
 that, as the whole thing really makes no sense to me.  I would prefer 
 right-to-left consistently, as the latter isn't intuitive:
 
     alias char [] string;
     string [int] bar; // Identical to the first definition of bar. Madness!
 
 This wasn't so important with C; arrays weren't useful [edit: and it 
 kind of made sense because declaration equaled usage].  But in D this is 
 really ugly.  Consistency please.
 
 Modern day edit: I consider this to be a design flaw in C running all 
 the way back to its genesis.  Types should be on the right:
 
     string : [] char;
 
 or better yet:
 
     string : array of (char);

May 21 2005
parent reply Burton Radons <burton-radons smocky.com> writes:
Unknown W. Brackets wrote:

 I'm not sure that's right.

Hence, "Here's what I wrote right before the change was adopted when it still worked as in C," showing why that way created problems (it was changed in DMD 0.54). It was a pain to parse too - you had to do a pre-parse and then reverse the order.
May 21 2005
parent "Unknown W. Brackets" <unknown simplemachines.org> writes:
Sorry, I missed that sentence; I noticed you didn't say that the 
reversal wasn't the solution, and I thought you were agreeing with it 
(while I believe it is wrong, because if you want char[] -> int -> value 
you should have it that way.)

Forgive me for my mistake.

-[Unknown]


 Unknown W. Brackets wrote:
 
 I'm not sure that's right.

Hence, "Here's what I wrote right before the change was adopted when it still worked as in C," showing why that way created problems (it was changed in DMD 0.54). It was a pain to parse too - you had to do a pre-parse and then reverse the order.

May 21 2005
prev sibling parent "Unknown W. Brackets" <unknown simplemachines.org> writes:
Actually, you're creating them wrong.

foo[char[]][int] myarray;

Means:

An array, indexed by integer, of...
An array, indexed by char[], of...
foos.

What you describe you want is:

An array, indexed by char[], of...
An array, indexed by integer, of...
foos.

Which means you want either:

foo[int][char[]] myarray;

Or:

foo myarray[char[]][int];

Remember: it's right-to-left on the left side, not left-to-right.

-[Unknown]


 MultiDimensional Associative Arrays
 
 Perhaps this is possible, and I don't know how to use it, but maybe it's not
 supported.
 
 if i want an array of class foo indexed by char[] and than by int..
 
 foo[char[]][int] myarray;
 
 so a structure looks like this...
 
 myarray
 {
 "one"
 {
 1
 2
 3
 }
 "two"
 {
 1
 2
 }
 "three"
 {
 1
 }
 "four"
 {
 1
 2
 3
 4
 }
 }
 
 i would access like this...
 
 myfoo = myarray["one"][1];
 
 and check to see if a member exists like this?
 
 foo[int]* name;
 name = ("one" in myarray);
 if(name != null)
 {
 foo[int]* value;
 value = (1 in name);
 if(value != null)
 {
 // value is a pointer to myarray["one"][1]
 }
 }
 
 Am I way off base? This doesn't compile right, but it made sense when i wrote
 it... The compiler thinks I am trying to "implicitly cast name of type char to
 int"
 
 Any and all help would be GREATLY appriciated.
 
 Thanks,
 Trevor Parscal
 www.trevorparscal.com
 trevorparscal hotmail.com

May 21 2005