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<H2><A NAME="SECTION02434000000000000000"></A><A NAME="ssec:basics:fundamental:enums"></A><A NAME="2186"></A><A NAME="2187"></A>
<BR>
Enumerations
</H2>
<P>
An enumeration is typically used in programming
languages to specify a limited range of states
to enable dealing with them by names instead of hard-coded values.
For language interoperability purposes -- especially to
support this concept on languages with no native support --
we've had to create specific rules for the integer values
associated with enumerated types.
<P>
<BR>
<PRE CLASS="verbatim">package enumSample version 1.0 {
// undefined integer values
enum color {
red, orange, yellow, green, blue, violet
};
// completely defined integer values
enum car {
/**
* A sports car.
*/
porsche = 911,
/**
* A family car.
*/
ford = 150,
/**
* A luxury car.
*/
mercedes = 550
};
// partially defined integer value
enum number {
notZero, // This non-doc comment will not be retained.
notOne,
zero=0,
one=1,
negOne=-1,
notNeg
};
}
</I></PRE></td></tr></table></blockquote>
<P>
Above is a sample of enumerations taken directly from
our regression tests. It defines a package <TT><I CLASS="slanted">enumSample</I></TT>
that contains three enumerations. C/C++ developers
will find the syntax very familiar.
When defining an enumeration, the actual integer values
assigned can be undefined, completely defined, or
partially defined.
<P>
SIDL defines the following rules for adding integer
values to enumerated states that don't have a value
explicitly defined.
<OL>
<LI>Error if two states are explicitly assigned the same value
</LI>
<LI>Assign all explicit values to their named state.
</LI>
<LI>Assign smallest unused non-negative value to first
unassigned state in enumeration.
</LI>
<LI>Repeat 3 until all states have assigned (unique) values.
</LI>
</OL>
<P>
To verify the application of these rules,
the <TT><I CLASS="slanted">enumSample.number</I></TT> enumeration
will have the following values assigned to
its states: <TT><I CLASS="slanted">NotZero</I></TT>=2, <TT><I CLASS="slanted">NotOne</I></TT>=3,
<TT><I CLASS="slanted">zero</I></TT>=0; <TT><I CLASS="slanted">one</I></TT>=1, <TT><I CLASS="slanted">negOne</I></TT>=-1,
<TT><I CLASS="slanted">notNeg</I></TT>=4.
<P>
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