Type conversion

The type conversion operator creates a property that converts an object of one built-in class to an object of another built-in class. The result belongs to the target built-in class. If type conversion is not possible, the property value will be NULL. An object of a user class is converted to a numeric or string class — the result is its internal identifier, an integer or its text form — and to the logical class, giving TRUE. There is no conversion to a user class: an object is found by its identifier with a grouping (see operation correctness), and a value narrowed to a user class is given by classification.

Supported conversions

Which conversions are meaningful depends on the built-in class families of the source and target classes:

• Within the family of numbers, the value is kept as far as the target class allows; when the value does not fit in the target class, the result is NULL.
• Between numbers and strings, the value is converted between its numeric and textual forms; when the source string cannot be read as a number of the target class, the result is NULL.
• Strings also convert to and from the JSON, JSONTEXT, XML, and HTML classes.

String and file types

String types can be converted to human-readable file types (CSVFILE, XMLFILE, JSONFILE, HTMLFILE, etc.), and vice versa - human-readable file types can be converted to string types. A file of a specific type can also be converted to a file of dynamic type (FILE, NAMEDFILE) and back, keeping the file content; the dynamic-type file additionally carries the extension, and NAMEDFILE also the name.

info

Dynamic-type files (FILE, NAMEDFILE) convert to strings and back directly: the file content is read as UTF-8 text (when it is not valid UTF-8 text, the result is NULL), and a string is written as the content of a file with the dat extension (a value of the HTML class — with the html extension). To get a different extension, convert the string to a file of a specific type first — for example, to CSVFILE, and only then to FILE: the resulting file will have the csv extension

Implicit conversions

Apart from the explicit conversion operator, the platform converts a value to another class implicitly in several contexts, without any conversion written by the developer:

• When values of different but compatible classes are combined — by addition or subtraction (see the arithmetic operators), by the selection operators, or by the extremum operators — each value is converted to their common ancestor, which becomes the result class; in particular, the number classes widen this way (an INTEGER combined with a NUMERIC becomes that NUMERIC).
• In string concatenation, an operand that is not a string is converted to a string.
• When a value is written to a property of a different but compatible class, it is converted to that class.
• A file of a specific type is converted to a file of dynamic type (FILE, NAMEDFILE) implicitly — for example during data import without a specified format, or when working with an external system; the resulting extension is determined as for the explicit conversion.

Language

To implement conversion, the type conversion operator is used.

Examples

itemCount = DATA INTEGER (Store);
itemCountToString(s) = BPSTRING[10](itemCount(s));

barcode = DATA STRING[15] (Item);
longBarcode(Item i) = LONG(barcode(i));