Mathematica: Webel ADT pseudo classes: POLICY: The expression '$$' is reserved as the primary named parameter for the defining pattern of all ADT classes that extend the universal base 'ADT' class.

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Note kind

POLICY

Policy level

STRICT

Webel Mathematica keywords

ADT`

Webel ADT

ADT⊙get

Keywords

Example:

ADT$Map[$$_Association]

ADT$Map /: get[$$_Association] := $$;

In the Webel recipe for ADTs this is actually inherited from a base ADT and uses a variable 'pattern' as a template that is passed to a definer function:

ADT /: get[pattern] := $$;

So in the above case pattern would be $$_Associaton.

This policy offers a clearly identified variable expression that is not likely to otherwise be used in code (unless deliberately) and helps avoid this possible clash:

Mathematica: GOTCHA: The Module/With system (especially under rewriting when nested) can leave variables with a trailing '$' suffix, which may cause name clashes because the variables (expressions) are available later outside the scope of the Module/With!

However, to make the Webel ADT recipe work when referenced from OTHER packages, you need this:

Mathematica: Webel ADT pseudo classes: A tricky POLICY & CONVENTION: Client packages MUST access the special "wrapped" primary '$$' via $ContextAliases! The recommended alias is "A`" (which stands of course for ADT).

Beware also that the special ADT⊙get accessor BREAKS ENCAPSULATION:

Mathematica: Webel ADT pseudo classes: The ADT⊙get method may be used to access the '$$' wrapped primary. This is intended for development and testing purposes only (not for regular use by clients) since it BREAKS ENCAPSULATION!

Relates to

Mathematica: POLICY NOTES for the Webel Abstract Data Type (ADT) pseudo classes with inheritance for the Wolfram Language

Introduction to Webel Abstract Data Types (ADTs) with SysMLv1 models

Mini SysMLv1 BDD view of the Webel ADT Block

SysMLv1 Internal Block Diagram (IBD) of the Webel ADT base class

Simple Webel ADT in the development view dV[adt] and class/methods help hC[adt]

Extending ADT sub-classes represented as SysML Blocks with redefined wrapped ‘$$’