Evaluation of variables - HiStructClient/femcad-doc GitHub Wiki

Do you wonder why you should use := or = in FemCad scripting?

The difference is in type of evaluation. Sign := stands for lazy evaluation and = stands for eager evaluation.

The author of FemCad suggest the following:

• for definition of main variables in gclass please use := (we might not need all the variables in gclass)
• inside dynamic objects, prefered is shorter = (the variable is evaluated during creation of object anyway)
• inside updaters, the suggested is shorter = (the variable is evaluated during creation of the called class anyway)
• if you are using .Aggregate function which uses updater in each iteration, please prefer the eager (=) evaluation, this prevents stacking of gclasses

The reason behind is the following:

= ... right hand side is evaluated immediately after loading of gclass, regardless the variable is used or not (eager evaluation)

:= ... right hand side is evaluated only in case some variable need the identifier on the left hand side (lazy evaluation)