Return Statements
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

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# 6.5 Return Statements

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

#### Syntax

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return_statement ::= return [expression];

#### Name Resolution Rules

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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

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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.
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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

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For the execution of a return_statement, the expression (if any) is first evaluated and converted to the result subtype.
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If the result type is class-wide, then the tag of the result is the tag of the value of the expression.
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If the result type is a specific tagged type:
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- 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.

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

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

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- a task or protected type;

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

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

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

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If the result type is a return-by-reference type, then a check is made that the return expression is one of the following:
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- a name that denotes an object view whose accessibility level is not deeper than that of the master that elaborated the function body; or

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

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The exception Program_Error is raised if this check fails.
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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.
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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

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Examples of return statements:
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`return; -- in a procedure body, entry_body, or accept_statement
return Key_Value(Last_Index); -- in a function body`

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