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digitalmars.D - Re: lazy thoughts

Andrei Alexandrescu Wrote:

 noobie wrote:
 Andrei Alexandrescu Wrote:
 int[] arr = [ 1, 2, 3, 4 ];
 auto squares = map!("a * a")(arr);
 arr[] = [ 5, 6, 7, 8 ];

 Now iterating squares will see different numbers than the original ones.

Okay, what is the problem in maintaining a reference to the original array values?

Efficiency. You'd have to copy the whole range, and in fact deep copy it. Andrei

Why can't it be done like copy-on-write? So all such functions would be lazy by default. Maybe on seeing code that modifies original values, a copy is created? Also with the current proposal I think its still better to provide two version than simply give the lazy func and .eager . Using standard lib functions should involve very little typing and the names make the code more legible. Thanks.
Jan 13 2009