| | | |
TOC -- / --.-- / --.--.-- | Index | Search | Syntax | Help

6.5 Return Statements

(1)

A return_statement is used to complete the execution of the innermost enclosing subprogram_body, entry_body, or accept_statement.

Syntax

(2)
       return_statement ::= return [expression];

Name Resolution Rules

(3)

The expression, if any, of a return_statement is called the return expression. The result subtype of a function is the subtype denoted by the subtype_mark after the reserved word return in the profile of the function. The expected type for a return expression is the result type of the corresponding function.

Legality Rules

(4)

A return_statement shall be within a callable construct, and it applies to the innermost one. A return_statement shall not be within a body that is within the construct to which the return_statement applies.

(5)

A function body shall contain at least one return_statement that applies to the function body, unless the function contains code_statements. A return_statement shall include a return expression if and only if it applies to a function body.

Dynamic Semantics

(6)

For the execution of a return_statement, the expression (if any) is first evaluated and converted to the result subtype.

(7)

If the result type is class-wide, then the tag of the result is the tag of the value of the expression.

(8)

If the result type is a specific tagged type:

(9)

• If it is limited, then a check is made that the tag of the value of the return expression identifies the result type. Constraint_Error is raised if this check fails.

(10)

• If it is nonlimited, then the tag of the result is that of the result type.

(11)

A type is a return-by-reference type if it is a descendant of one of the following:

(12)

• a tagged limited type;

(13)

• a task or protected type;

(14)

• a nonprivate type with the reserved word limited in its declaration;

(15)

• a composite type with a subcomponent of a return-by-reference type;

(16)

• a private type whose full type is a return-by-reference type.

(17)

If the result type is a return-by-reference type, then a check is made that the return expression is one of the following:

(18)

• a name that denotes an object view whose accessibility level is not deeper than that of the master that elaborated the function body; or

(19)

• a parenthesized expression or qualified_expression whose operand is one of these kinds of expressions.

(20)

The exception Program_Error is raised if this check fails.

(21)

For a function with a return-by-reference result type the result is returned by reference; that is, the function call denotes a constant view of the object associated with the value of the return expression. For any other function, the result is returned by copy; that is, the converted value is assigned into an anonymous constant created at the point of the return_statement, and the function call denotes that object.

(22)

Finally, a transfer of control is performed which completes the execution of the callable construct to which the return_statement applies, and returns to the caller.

Examples

(23)

Examples of return statements:

(24)
       return;                         -- in a procedure body, entry_body, or accept_statement
       return Key_Value(Last_Index);   -- in a function body

| | | |
TOC -- / --.-- / --.--.-- | Index | Search | Syntax | Help

-- Email comments, additions, corrections, gripes, kudos, etc. to: