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digitalmars.D.learn - Associative array for array of classes

reply clayasaurus <clayasaurus gmail.com> writes:
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Ok, for basic types I know I can use

int[char[]] assoc;
assoc["3"] = 3;

And for classes I can do.

Class[char[]] assoc;
assoc["3"] = new Class;

Now, lets say I want to test if assoc["3"] has already been initialized 
before I allocate it, but testing it with

if (assoc["3"] is null)
   assoc["3"] = new Class;

I get a seg fault. Any other way to do this? File attached to better 
illustrate my problem. Thanks.

~ Clay
Apr 26 2006
next sibling parent reply Derek Parnell <derek psych.ward> writes:
On Wed, 26 Apr 2006 23:49:07 -0500, clayasaurus wrote:


 import std.stdio;
 
 int main()
 {
 	char[] i = "3";
 
 	int[char[]] assoc;
 	assoc[i] = 3;
 
 	Class[char[]] assoc2;
 
 	// doesn't work
 	if (assoc2[i] is null)
 		assoc2[i] = new Class;
 
 	// works
 	assoc2[i] = new Class;
 
 	writefln("hi");
 
 	return 0;
 }
 
 class Class
 {
   public:
 	this(){}
 	int x,y;
 }



Try this ...

  if (!(i in assoc2))
    assoc2[i] = new Class;

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
27/04/2006 3:09:47 PM
Apr 26 2006
parent clayasaurus <clayasaurus gmail.com> writes:
Derek Parnell wrote:

 On Wed, 26 Apr 2006 23:49:07 -0500, clayasaurus wrote:
 
 Try this ...
 
   if (!(i in assoc2))
     assoc2[i] = new Class;
 



Thanks :) That seems to do the trick.
Apr 26 2006
prev sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
clayasaurus wrote:
<snip>

 Class[char[]] assoc;
 assoc["3"] = new Class;
 
 Now, lets say I want to test if assoc["3"] has already been initialized 
 before I allocate it, but testing it with
 
 if (assoc["3"] is null)
   assoc["3"] = new Class;
 
 I get a seg fault.




That's strange.  It should be an ArrayBoundsError.

Stewart.
Apr 27 2006
parent reply "Alberto Simon" <lugaidster gmail.com> writes:
You should use '(("3" in assoc) == null)' instead of '(assoc["3"] is null)'

Regards,
Alberto Simon
"Stewart Gordon" <smjg_1998 yahoo.com> escribió en el mensaje 
news:e2qh6d$1lfk$2 digitaldaemon.com...

 clayasaurus wrote:
 <snip>

 Class[char[]] assoc;
 assoc["3"] = new Class;

 Now, lets say I want to test if assoc["3"] has already been initialized 
 before I allocate it, but testing it with

 if (assoc["3"] is null)
   assoc["3"] = new Class;

 I get a seg fault.




 That's strange.  It should be an ArrayBoundsError.

 Stewart.
Apr 27 2006
parent reply Sean Kelly <sean f4.ca> writes:
The correct use of AAs is so intuitive I'm amazed anyone ever gets it 
wrong.  It's times like this when I wish I'd been more vocal about 
actually liking the old syntax :-p


Alberto Simon wrote:

 You should use '(("3" in assoc) == null)' instead of '(assoc["3"] is null)'
 
 Regards,
 Alberto Simon
 "Stewart Gordon" <smjg_1998 yahoo.com> escribió en el mensaje 
 news:e2qh6d$1lfk$2 digitaldaemon.com...

 clayasaurus wrote:
 <snip>

 Class[char[]] assoc;
 assoc["3"] = new Class;

 Now, lets say I want to test if assoc["3"] has already been initialized 
 before I allocate it, but testing it with

 if (assoc["3"] is null)
   assoc["3"] = new Class;

 I get a seg fault.




 That's strange.  It should be an ArrayBoundsError.

 Stewart.
Apr 27 2006
parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Sean Kelly wrote:

 The correct use of AAs is so intuitive I'm amazed anyone ever gets it 
 wrong.  It's times like this when I wish I'd been more vocal about 
 actually liking the old syntax :-p




What old syntax?

The in operator has always been the correct way to check whether an AA 
contains a given key.  Looking it up and comparing it against 
valuetype.init was never a general solution.  And

     if ("3" in assoc)

or

     if (!("3" in assoc))

still works just the same.

[F'up back to d.D.learn]

Stewart.
Apr 28 2006