Removing entries from AAs

[Timon Gehr]

On 08/19/2011 02:01 PM, useo6 wrote:
> Hi,
>
> I've create a little example of my problem:
>
> module example;
>
> class ExampleClass {
>
> 	public {
>
> 		int mi;
>
> 		this(int i) {
> 			mi = i;
> 		}
>
> 	}
>
> }
>
> int main(string[] args) {
>
> 	ExampleClass[hash_t] exp;
>
> 	ExampleClass cex = new ExampleClass(1);
> 	exp[cex.toHash()] = cex;
>
> 	cex = new ExampleClass(2);
> 	exp[cex.toHash()] = cex;
>
> 	cex = new ExampleClass(3);
> 	exp[cex.toHash()] = cex;
>
> 	foreach (ExampleClass c; exp) {
> 		if (c.mi == 2) {exp.remove(c.toHash()); }
> 	}
>
> 	return 0;
>
> }
>
> When I run this small example-app, I get an "Access Violation". When
> I insert a break into my foreach-loop like:
>
> 	foreach (ExampleClass c; exp) {
> 		if (c.mi == 2) {exp.remove(c.toHash()); break; }
> 	}
>
> it works, but this means, I leave the foreach-loop. What I'm doing
> wrong by using the foreach-block?
>
> Thanks for any help!

The problem is that you change the AA while iterating over it. You could 
eg iterate over it and save all keys you want to remove into an array 
and then iterate over the array to remove the keys from the AA.

This works:


module example;

class ExampleClass {

	public {

		int mi;

		this(int i) {
			mi = i;
		}

	}

}

int main(string[] args) {

	ExampleClass[hash_t] exp;

	ExampleClass cex = new ExampleClass(1);
	exp[cex.toHash()] = cex;

	cex = new ExampleClass(2);
	exp[cex.toHash()] = cex;

	cex = new ExampleClass(3);
	exp[cex.toHash()] = cex;

	hash_t[] toRemove;
	
	foreach (c; exp) {
		if (c.mi == 2) { toRemove~=c.toHash(); }
	}
	foreach (h; toRemove) {
		exp.remove(h);
	}

	return 0;

}