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<?xml version="1.0"?>
<clause number="18.4.1" title="Database integer type" informative="true">
<paragraph>The DBInt struct below implements an integer type that can represent the complete set of values of the <keyword>int</keyword> type, plus an additional state that indicates an unknown value. A type with these characteristics is commonly used in databases. <code_example><![CDATA[
using System;
public struct DBInt
{
// The Null member represents an unknown DBInt value.
public static readonly DBInt Null = new DBInt();
// When the defined field is true, this DBInt represents a known value
// which is stored in the value field. When the defined field is false,
// this DBInt represents an unknown value, and the value field is 0.
int value;
bool defined;
// Private instance constructor. Creates a DBInt with a known value.
DBInt(int value) {
this.value = value;
this.defined = true;
}
// The IsNull property is true if this DBInt represents an unknown value.
public bool IsNull { get { return !defined; } }
// The Value property is the known value of this DBInt, or 0 if this
// DBInt represents an unknown value.
public int Value { get { return value; } }
// Implicit conversion from int to DBInt.
public static implicit operator DBInt(int x) {
return new DBInt(x);
}
// Explicit conversion from DBInt to int. Throws an exception if the
// given DBInt represents an unknown value.
public static explicit operator int(DBInt x) {
if (!x.defined) throw new InvalidOperationException();
return x.value;
}
public static DBInt operator +(DBInt x) {
return x;
}
public static DBInt operator -(DBInt x) {
return x.defined? -x.value: Null;
}
public static DBInt operator +(DBInt x, DBInt y) {
return x.defined && y.defined? x.value + y.value: Null;
}
public static DBInt operator -(DBInt x, DBInt y) {
return x.defined && y.defined? x.value - y.value: Null;
}
public static DBInt operator *(DBInt x, DBInt y) {
return x.defined && y.defined? x.value * y.value: Null;
}
public static DBInt operator /(DBInt x, DBInt y) {
return x.defined && y.defined? x.value / y.value: Null;
}
public static DBInt operator %(DBInt x, DBInt y) {
return x.defined && y.defined? x.value % y.value: Null;
}
public static DBBool operator ==(DBInt x, DBInt y) {
return x.defined && y.defined? x.value == y.value: DBBool.Null;
}
public static DBBool operator !=(DBInt x, DBInt y) {
return x.defined && y.defined? x.value != y.value: DBBool.Null;
}
public static DBBool operator >(DBInt x, DBInt y) {
return x.defined && y.defined? x.value > y.value: DBBool.Null;
}
public static DBBool operator <(DBInt x, DBInt y) {
return x.defined && y.defined? x.value < y.value: DBBool.Null;
}
public static DBBool operator >=(DBInt x, DBInt y) {
return x.defined && y.defined? x.value >= y.value: DBBool.Null;
}
public static DBBool operator <=(DBInt x, DBInt y) {
return x.defined && y.defined? x.value <= y.value: DBBool.Null;
}
}
]]></code_example></paragraph>
</clause>
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