Collections are a new data type, and as such they will come with some learning curve but if given the time will prove to be a valuable asset to developing in 4D. One such curve to learn is using a collection with a for-loop.

When stepping through an array in a for-loop, the code looks like this:

For ($i;1;Size of array($some_array))     // do something with array values   $arr_val:=$some_array{$i} End for

When stepping through a collection, the for-loop is setup slightly differently because, unlike the array, the collection starts indexing at "0" instead of "1":

For ($i;0;$some_collection.length-1)     // do something with collection values   $col_val:=$some_collection[$i] End for

Important in the above is to have object notation turned on, as the built in length property of the collection is used as the end value of the for-loop, in place of the Size of array command used with arrays.

So why iterate the for-loop from 0 to length-1?

This is because the collection starts the index at 0, which is also counted in the length, so the last index of the collection for a collection with 5 elements would be 4, hence why length-1 is used to end the for-loop.

Alternatively, the for-loop for the collection could be written like this to achieve the same results:

For ($i;1;$some_collection.length)     // do something with collection values   $col_val:=$some_collection[$i-1] End for

In version 17, there will be yet another way to loop through a collection using a new statement For each/End for each. Example below, each element of the collection is iterated through and returned in the $item variable:

For each($item;$some_collection)     // do something with collection values   $col_val:=$item End for each