• Indexed references

1.  The NetRexx language introduced the ability to index array-like objects with square brackets.

2.  roo!™ also uses square brackets to reference composite object values.

3.  Indexing within roo!™ programs is somewhat similar, but may differ from the NetRexx technique.

4.  Unlike NetRexx, indexing within roo!™ programs uses an approach which is more similar to that used in C, C++, Java, or C# programs.

5.  For example, roo!™ programs can use nested and cascading index references.

6.  Arbitrary composite items can be indexed with square brackets.

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7.  Square brackets can be used to reference or revise classes that are derived from the aggregate built-in class.

8.  The expression

         obj [ indexValue ]

9.  can be used wherever a term is expected in a Rexx expression.

10.  This reference is a shorthand equivalent to:

          obj ~ getAt( indexValue )

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11.  If the item which precedes the left square bracket is not an instance, the reference is transformed into a compound symbol reference instead.

12.  This emulates a NetRexx indexed string reference, with one index value.

13.  In this case, the reference is similar to:

          obj.indexValue

14.  The instruction is actually equivalent to the result of the following value built-in function request:

          value( 'OBJ.' || indexValue, newValue )

15.  Where:

          indexValue may be a compound variable.

16.  Observe: if the compound variable is not assigned a value, the value of simple symbol obj becomes the value of the reference.

17.  This differs from the normal Rexx value that is substituted for an unassigned compound variable.

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18.  Similarly, square brackets can be used within the value that precedes an assignment expression (=).

19.  The expression

          obj [ indexValue ] = newValue

20.  is a shorthand equivalent to:

          obj ~ setAt( indexValue, newValue )

21.  If the item which precedes the left square bracket is not an instance, the reference is transformed into a compound symbol reference instead.

22.  In this case, the instruction is similar to:

          obj.indexValue = newValue

23.  The instruction is actually equivalent to:

          call value 'OBJ.' || indexValue, newValue

24.  Where:

          indexValue may be a compound variable.

25.  Note: recognition of an assignment instruction is enhanced to search for the equal sign that follows a bracketed reference.

26.  The expression on the left side of the equal sign can have a cascade of square bracket expressions as well.

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27.  Note: array references can be nested, for example:

          obj [ obj2[ indexValue ] ]

28.  Note: array references can be performed in sequence, for example:

          obj [ indexValue1 ] [ indexValue2 ]

29.  Note: the expression within the square brackets is evaluated as though the square brackets were parentheses.