Modifying Action Diagrams › Understanding Contexts › Function Contexts › ARR › Multiple-instance Arrays and the ARR Context

Multiple-instance Arrays and the ARR Context

Arrays are a standard component of the 2E model that you might have utilized in the past. An array is a structure, comprised of multiple fields (array subfields), that has a specified number of elements. Arrays are defined in the *Arrays file.

Prior to release 8.6, there were three ways to use an array:

• Through the use of CHGOBJ, CRTOBJ, DLTOBJ, and RTVOBJ functions built over an array to process data in the array, treating the array as if it were an access path, where each element of the array equates to a record.
• As a structure that can be used to pass parameters to a function.
• With the *CVTVAR built-in function, you can compose a single string from an array structure of multiple fields. You can also decompose a single string into its constituent fields.

  For more information on these functions, see the Building Applications Guide and the Command Reference Guide.

With the second and third uses, only a single instance of the array structure was referred to – the array was being used only as a structure definition, in other words.

With Release 8.6, we increased the ways you can use arrays:

• Treat an array as a multiple instance structure. In other words, as a true array with multiple elements within the Action Diagram. In this case use the new *MOVE ARRAY function – individual fields in a variety of contexts can be copied into array subfields in a specified instance of the array and vice-versa.
• Pass a multiple-instance array as a parameter to a function. By passing a parameter in this way, you can pass multiple instances of data in or out as a single parameter, in a single call to a function.

Important! As a CA 2E developer, you need to understand the architectural distinction between the two mechanisms to manipulate array data, despite the ability to use a common structural definition:

• Data can exist and be modified in an array by using database functions (Create Object – CRTOBJ, Delete Object –DLTOBJ, Change Object – CHGOBJ, and Retrieve Object – RTVOBJ) based over the *Arrays file. However, this array data cannot be accessed by the *MOVE ARRAY function.
• Conversely, data can exist and be modified in a multiple-instance array parameter (in the PAR context) and in the ARR context by using the *MOVE ARRAY function. However, that array data cannot be accessed by database functions (Create Object – CRTOBJ, Delete Object –DLTOBJ, Change Object – CHGOBJ, and Retrieve Object – RTVOBJ) based over the *Arrays file.

To make this new functionality possible, we created a new array-related context, ARR context. The ARR context is similar to the WRK context, but is used to define a multiple-instance array. Similar to fields in the WRK context, arrays in the ARR context are initialized during program initialization.The ARR context is available in the following circumstances:

• For use with the *MOVE ARRAY built-in function.
• When passing a multiple-instance array to a function that has a multiple-instance array parameter. For more details, see Enhanced Array Support.