78 lines
3.3 KiB
XML
78 lines
3.3 KiB
XML
<?xml version="1.0"?>
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<clause number="18.4.1" title="Database integer type" informative="true">
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<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[
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using System;
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public struct DBInt
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{
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// The Null member represents an unknown DBInt value.
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public static readonly DBInt Null = new DBInt();
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// When the defined field is true, this DBInt represents a known value
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// which is stored in the value field. When the defined field is false,
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// this DBInt represents an unknown value, and the value field is 0.
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int value;
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bool defined;
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// Private instance constructor. Creates a DBInt with a known value.
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DBInt(int value) {
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this.value = value;
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this.defined = true;
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}
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// The IsNull property is true if this DBInt represents an unknown value.
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public bool IsNull { get { return !defined; } }
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// The Value property is the known value of this DBInt, or 0 if this
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// DBInt represents an unknown value.
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public int Value { get { return value; } }
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// Implicit conversion from int to DBInt.
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public static implicit operator DBInt(int x) {
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return new DBInt(x);
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}
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// Explicit conversion from DBInt to int. Throws an exception if the
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// given DBInt represents an unknown value.
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public static explicit operator int(DBInt x) {
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if (!x.defined) throw new InvalidOperationException();
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return x.value;
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}
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public static DBInt operator +(DBInt x) {
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return x;
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}
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public static DBInt operator -(DBInt x) {
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return x.defined? -x.value: Null;
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}
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public static DBInt operator +(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value + y.value: Null;
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}
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public static DBInt operator -(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value - y.value: Null;
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}
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public static DBInt operator *(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value * y.value: Null;
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}
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public static DBInt operator /(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value / y.value: Null;
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}
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public static DBInt operator %(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value % y.value: Null;
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}
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public static DBBool operator ==(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value == y.value: DBBool.Null;
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}
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public static DBBool operator !=(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value != y.value: DBBool.Null;
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}
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public static DBBool operator >(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value > y.value: DBBool.Null;
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}
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public static DBBool operator <(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value < y.value: DBBool.Null;
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}
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public static DBBool operator >=(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value >= y.value: DBBool.Null;
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}
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public static DBBool operator <=(DBInt x, DBInt y) {
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return x.defined && y.defined? x.value <= y.value: DBBool.Null;
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}
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}
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]]></code_example></paragraph>
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</clause>
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