foreach - premature optimization vs cultivating good habits

[Laeeth Isharc via Digitalmars-d-learn]

Hi.

The standard advice is not to worry about memory usage and 
execution speed until profiling shows you where the problem is, 
and I respect Knuth greatly as a thinker.

Still, one may learn from others' experience and cultivate good 
habits early.  To say that one should not prematurely optimize is 
not to say that one should not try to avoid cases that tend to be 
really bad, and I would rather learn from others what these are 
then learn only the hard way.

For the time being I am still at early development stage and have 
not yet tested things with the larger data sets I anticipate 
eventually using.  It's cheap to make slightly different design 
decisions early, but much more painful further down the line, 
particularly given my context.

As I understand it, foreach allocates when a simple C-style for 
using an array index would not.  I would like to learn more about 
when this turns particularly expensive, and perhaps I could put 
this up on the wiki if people think it is a good idea.

What exactly does it allocate, and how often, and how large is 
this in relation to the size of the underlying data 
(structs/classes/ranges)?  Are there any cache effects to 
consider?  Happy to go to the source code if you can give me some 
pointers.

Thanks in advice for any thoughts.



Laeeth.