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copied!<p>Because fred is not a boolean. it is a struct, which has a boolean property called IsNull, or HasValue, or whatever... The object named fred is the complex composite object containing a boolean and a value, not a primitive boolean itself... </p> <p>Below, for example is how a Nullable Int could be implemented. The generic Nullable is almost certainly implemented similarly (but generically). You can see here how the implicit and explicit conversions are implemented..</p> <pre><code>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; } public override bool Equals(object o) { try { return (bool) (this == (DBInt) o); } catch { return false; } } public override int GetHashCode() { return (defined)? value: 0; } public override string ToString() { return (defined)? .ToString(): "DBInt.Null"; } } </code></pre>

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