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digitalmars.D - Associative Array of structs

reply Zane <zane.sims gmail.com> writes:
I tried writing to an associative array and got the exception:

tango.core.Exception.ArrayBoundsException test(15): Array index out of bounds

the program below causes the exception:

module test;

import tango.io.Stdout;
import tango.io.Console;
	
struct S {uint i;}
		
int main()
{
	S[char[]] s;
	
	s["test"].i = 1;	

	Stdout.format("Done!").flush;

	return 0;
}

But the program below works fine:

module test;

import tango.io.Stdout;
import tango.io.Console;
	
struct S {uint i;}
		
int main()
{
	S[char[]] s;
	
	S t;
	t.i = 1;
		
	s["test"] = t;

	Stdout.format("Done!").flush;

	return 0;
}

Am I supposed to be able to do both methods, or is the second the only possible
way?  Some explanation would be very helpful.

Thanks for your time,
Zane
Dec 02 2008
next sibling parent "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Tue, Dec 2, 2008 at 7:34 PM, Zane <zane.sims gmail.com> wrote:
 I tried writing to an associative array and got the exception:

 tango.core.Exception.ArrayBoundsException test(15): Array index out of bounds

 the program below causes the exception:

 module test;

 import tango.io.Stdout;
 import tango.io.Console;

 struct S {uint i;}

 int main()
 {
        S[char[]] s;

        s["test"].i = 1;

        Stdout.format("Done!").flush;

        return 0;
 }

 But the program below works fine:

 module test;

 import tango.io.Stdout;
 import tango.io.Console;

 struct S {uint i;}

 int main()
 {
        S[char[]] s;

        S t;
        t.i = 1;

        s["test"] = t;

        Stdout.format("Done!").flush;

        return 0;
 }

 Am I supposed to be able to do both methods, or is the second the only
possible way?  Some explanation would be very helpful.

Only the second is legal. The first is doing something like this: auto temp = &s["test"]; temp.i = 1; Of course, you haven't added anything to s yet, so s["test"] fails with an out-of-bounds error. It's a little awkward, and in fact long ago, AAs used to implicitly add items when accessing undefined indices (but many people found that unintuitive and the behavior was changed to what it is now). It's not too much work to make an AA wrapper struct which overloads opIndex[Assign] and allows you to do this, by adding key-value pairs if they don't already exist.
Dec 02 2008
prev sibling next sibling parent "Denis Koroskin" <2korden gmail.com> writes:
03.12.08 в 03:55 Jarrett Billingsley в своём письме писал(а):

 On Tue, Dec 2, 2008 at 7:34 PM, Zane <zane.sims gmail.com> wrote:
 I tried writing to an associative array and got the exception:

 tango.core.Exception.ArrayBoundsException test(15): Array index out of  
 bounds

 the program below causes the exception:

 module test;

 import tango.io.Stdout;
 import tango.io.Console;

 struct S {uint i;}

 int main()
 {
        S[char[]] s;

        s["test"].i = 1;

        Stdout.format("Done!").flush;

        return 0;
 }

 But the program below works fine:

 module test;

 import tango.io.Stdout;
 import tango.io.Console;

 struct S {uint i;}

 int main()
 {
        S[char[]] s;

        S t;
        t.i = 1;

        s["test"] = t;

        Stdout.format("Done!").flush;

        return 0;
 }

 Am I supposed to be able to do both methods, or is the second the only  
 possible way?  Some explanation would be very helpful.

Only the second is legal. The first is doing something like this: auto temp = &s["test"];

Correction: auto temp = "test" in s;
 temp.i = 1;

 Of course, you haven't added anything to s yet, so s["test"] fails
 with an out-of-bounds error.

 It's a little awkward, and in fact long ago, AAs used to implicitly
 add items when accessing undefined indices (but many people found that
 unintuitive and the behavior was changed to what it is now).

 It's not too much work to make an AA wrapper struct which overloads
 opIndex[Assign] and allows you to do this, by adding key-value pairs
 if they don't already exist.

Dec 03 2008
prev sibling parent "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Wed, Dec 3, 2008 at 4:36 AM, Denis Koroskin <2korden gmail.com> wrote:
 Correction:
 auto temp = "test" in s;

'in' does not give an array bounds error.
Dec 03 2008