Explicit Offsets

Section - TM Language Reference

These provide a mechanism for explicitly reading values within a path. They differ from Indexes in being expressed numerically:

An explicit offset --       statement[2].name

An index --                    Relationship[idx].Attribute

Explicit offsets, which should only be used when attempting to read a value, are very simple. For example:

statement[2].name

means take the second item in the path called statement (where statement is an aggregate). If statement does not contain two items it won't return anything.

Explicit offsets may be used in succession. For example:

statement[2].part[4].item

takes the second statement, looks for the fourth part and then returns the item.

It is permissible to end a line with an explicit offset.  For example:

This, however, has the same effect as:

aItem := statement.$getIntance2;

Notes:

• XPaths behind the relationship can be used to select 2nd, 3rd or 4th items and so on, but if this is done the relationship should be named appropriately (for example, getSecondStatement) or the Transform will be harder to maintain and less useful as a document.
• Variables cannot be used with explicit offsets; use iteration instead.
• Setting explicit offsets in the target is not permitted.
• All counting in SML starts from 1.