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User Types

Summary:

• Definition
• Syntax
• Usage
• Examples

See also: Variables, Records, Data Types, Constants.

Definition

A user type is a data type based on built-in types, records or arrays. It can be used as a synonym for a single base type or structured types.

You typically define a user type for structured types (i.e. records), so it can be reused as a single word at many places in the code:

01 TYPE customer RECORD
02        cust_num INTEGER,
03        cust_name VARCHAR(50),
04        cust_addr VARCHAR(200)
05     END RECORD

A good practice is to define user types that belong to the same domain in a single .4gl module, and import that module in the modules where the types are needed.

Syntax

Syntax:

where type-definition is:

Notes:

1. identifier is the name of the user type to be defined.
2. definition is any data type, record structure, or array definition supported by the language.

Usage

You can define a user type as a synonym for an existing data type, or as a shortcut for records and array structures.

After declaring a user type, it can be used as a normal data type to define variables.

The scope of a user type is the same as for variables and constants. Types can be global, module-specific, or local to a function.

By default, module-specific types are private; They cannot be used by an other module of the program. To make a module type public, add the PUBLIC keyword before TYPE. When a module type is declared as public, it can be referenced by another module by using the IMPORT instruction.

Examples

Example 1:

01 TYPE customer RECORD
02        cust_num INTEGER,
03        cust_name VARCHAR(50),
04        cust_addr VARCHAR(200)
05     END RECORD
06 DEFINE c customer

Example 2:

The following example defines a user type in first module, and then uses the type in a report program:

01 -- type_order.4gl
02
04 PUBLIC TYPE rpt_order RECORD
05        order_num  INTEGER,
06        store_num  INTEGER,
07        order_date DATE,
08        cust_num INTEGER,
09        fac_code   CHAR(3)
10     END RECORD

01 -- report.4gl
02
03 IMPORT FGL type_order
04
05 MAIN
06   DEFINE o rpt_order  -- could be type_order.rpt_order
07   CONNECT TO "custdemo"
08   DECLARE order_c CURSOR FOR
09     SELECT orders.*
10       FROM orders ORDER BY cust_num
11   START REPORT order_list 
12   FOREACH order_c INTO o.*
13     OUTPUT TO REPORT order_list(o.*)
14   END FOREACH
15   FINISH REPORT order_list
16   DISCONNECT CURRENT
17 END MAIN 
18
19 REPORT order_list(ro)
20   DEFINE ro rpt_order
21   FORMAT
22     ON EVERY ROW
23      PRINT ro.order_num, ...
...