Best practice for creating objects used in for/foreach loops

Question

What's the best practice for dealing with objects in for or foreach loops? Should we create one object outside the loops and recreate it all over again (using new... ) or create new one for every loop iteration?
Example:

foreach(var a in collection) {   SomeClass sc = new SomeClass();   sc.id = a;   sc.Insert(); } 

or

SomeClass sc = null; foreach(var a in collection) {   sc = new SomeClass();   sc.id = a;   sc.Insert(); } 

Which is better?

Answer 1

The first way is better as it more clearly conveys the intended scope of the variable and prevents errors from accidentally using an object outside of the intended scope.

One reason for wanting to use the second form is if you want to break out of the loop and still have a reference to the object you last reached in the loop.

A bad reason for choosing the second form is performance. It might seem at first glance that the second method uses fewer resources or that you are only creating one object and reusing it. This isn't the case here. The repeated declaration of a variable inside a loop doesn't consume any extra resources or clock cycles so you don't gain any performance benefit from pulling the declaration outside the loop.