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4.3 Sharing data

As mentioned in the beginning of this chapter, the assignment operator (=) does not copy anything when you use it on a pointer type. Instead it just creates another reference to the memory object. In most situations this does not present a problem, and it speeds up Pike's performance. However, you must be aware of this when programming. This can be illustrated with an example: 
int main(int argc, array(string) argv)
{
    array(string) tmp;
    tmp=argv;
    argv[0]="Hello world.\n";
    write(tmp[0]);
}
This program will of course write Hello world.

Sometimes you want to create a copy of a mapping, array or object. To do so you simply call copy_value with whatever you want to copy as argument. Copy_value is recursive, which means that if you have an array containing arrays, copies will be made of all those arrays.

If you don't want to copy recursively, or you know you don't have to copy recursively, you can use the plus operator instead. For instance, to create a copy of an array you simply add an empty array to it, like this: copy_of_arr = arr + ({}); If you need to copy a mapping you use an empty mapping, and for a multiset you use an empty multiset.

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