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<H1> 6.5 Return Statements</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">return_statement</FONT>
is used to complete the execution of the innermost enclosing <FONT FACE="Arial, Helvetica">subprogram_body</FONT>,
<FONT FACE="Arial, Helvetica">entry_body</FONT>, or <FONT FACE="Arial, Helvetica">accept_statement</FONT>.
</DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">return_statement<A NAME="I3029"></A>
::= </FONT><B>return</B> [<A NAME="I3030"></A><FONT FACE="Arial, Helvetica">expression</FONT>];</DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3031"></A>The <FONT FACE="Arial, Helvetica">expression</FONT>,
if any, of a <FONT FACE="Arial, Helvetica">return_statement</FONT> is
called the <I>return expression</I>. <A NAME="I3032"></A>The <I>result
subtype</I> of a function is the subtype denoted by the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>
after the reserved word <B>return</B> in the profile of the function.
<A NAME="I3033"></A>The expected type for a return expression is the
result type of the corresponding function. </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3034"></A>A <FONT FACE="Arial, Helvetica">return_statement</FONT>
shall be within a callable construct, and it <I>applies to</I> the innermost
one. A <FONT FACE="Arial, Helvetica">return_statement</FONT> shall not
be within a body that is within the construct to which the <FONT FACE="Arial, Helvetica">return_statement</FONT>
applies.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> A function body shall contain at least one <FONT FACE="Arial, Helvetica">return_statement</FONT>
that applies to the function body, unless the function contains <FONT FACE="Arial, Helvetica">code_statement</FONT>s.
A <FONT FACE="Arial, Helvetica">return_statement</FONT> shall include
a return expression if and only if it applies to a function body. </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3035"></A>For the execution of a <FONT FACE="Arial, Helvetica">return_statement</FONT>,
the <FONT FACE="Arial, Helvetica">expression</FONT> (if any) is first
evaluated and converted to the result subtype. <A NAME="I3036"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> If the result type is class-wide, then the tag
of the result is the tag of the value of the <FONT FACE="Arial, Helvetica">expression</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> If the result type
is a specific tagged type: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC><A NAME="I3037"></A><A NAME="I3038"></A>If it is limited,
then a check is made that the tag of the value of the return expression
identifies the result type. <A NAME="I3039"></A>Constraint_Error is raised
if this check fails.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>If it is nonlimited, then the tag of the result is that
of the result type. </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <A NAME="I3040"></A>A
type is a <I>return-by-reference</I> type if it is a descendant of one
of the following: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a tagged limited type;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a task or protected type;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a nonprivate type with the reserved word <B>limited</B>
in its declaration;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a composite type with a subcomponent of a return-by-reference
type;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a private type whose full type is a return-by-reference
type. </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <A NAME="I3041"></A><A NAME="I3042"></A>If
the result type is a return-by-reference type, then a check is made that
the return expression is one of the following: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a <FONT FACE="Arial, Helvetica">name</FONT> that denotes
an object view whose accessibility level is not deeper than that of the
master that elaborated the function body; or</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>a parenthesized expression or <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
whose operand is one of these kinds of expressions.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3043"></A>The exception Program_Error
is raised if this check fails. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Normal"> 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. <A NAME="I3044"></A>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 <FONT FACE="Arial, Helvetica">return_statement</FONT>,
and the function call denotes that object. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Normal"> Finally, a transfer of control is performed which
completes the execution of the callable construct to which the <FONT FACE="Arial, Helvetica">return_statement</FONT>
applies, and returns to the caller. </DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
return statements:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Examples"><TT><B>return</B>; --<I> in a procedure body, <FONT FACE="Arial, Helvetica">entry_body</FONT>, or <FONT FACE="Arial, Helvetica">accept_statement</FONT></I><BR>
<B>return</B> Key_Value(Last_Index); --<I> in a function body</I></TT></DIV>
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