RETURN operator

The RETURN operator creates an action that implements exit from an action call.

Syntax

RETURN [resultExpr]

Description

The RETURN operator creates an action that exits from the innermost enclosing action call. If resultExpr is specified, its value becomes the result of that call. Otherwise the call simply exits without producing a value.

The result class of the surrounding action is determined in one of two ways:

• For abstract actions, the result class is declared in the ABSTRACT operator; the value class of resultExpr must conform to the declared class.
• For other actions, the result class is inferred from resultExpr of all RETURN operators in the body. If several RETURN operators are present, the resulting class is the common ancestor of the classes of their expression values.

If the platform cannot determine the value class of resultExpr, such a RETURN is invalid. For example, the class cannot be inferred from an untyped NULL value.

If resultExpr declares new local parameters, they become additional parameters of the result. In this case the action returns a set of objects depending on the values of those parameters.

A bare RETURN is allowed in any action regardless of whether the action declares a result.

Parameters

• resultExpr

  Optional expression. Its value is returned to the caller as the result of the surrounding action. For abstract actions, the value class of this expression must conform to the declared result class. For other actions, the platform must be able to infer this class.

Examples

// bare RETURN — exits the surrounding action without producing a value
importFile  {
    LOCAL file = FILE ();
    INPUT f = FILE DO {
        file () <- f;
    }

    IF NOT file() THEN RETURN;
}

// RETURN with an expression — result class is inferred from the expressions
priceBucket (INTEGER price)  {
    IF price > 1000 THEN RETURN 'high';
    IF price > 100 THEN RETURN 'mid';
    RETURN 'low';
}

// an extra parameter in the expression — the action returns a set of values indexed by that parameter
allCaptions ()  {
    LOCAL caption = STRING[100] (STRING);
    caption('A') <- 'Alpha';
    caption('B') <- 'Beta';
    RETURN caption(STRING s);
}

// RETURN with an expression in an abstract action with a declared result class
getLocalizedTitle(Issue issue) ABSTRACT STRING[100] (Language);
getLocalizedTitle (Issue issue) + {
    RETURN localizedTitle(issue, Language l);
}