New Core Tutorial

git-svn-id: svn://ultimatepp.org/upp/trunk@10538 f0d560ea-af0d-0410-9eb7-867de7ffcac7

tutorial/CoreTutorial/Null.cpp

@@ -0,0 +1,44 @@
+#include "Tutorial.h"
+
+void NullTutorial()
+{
+	/// .`Null`
+	
+	/// U++ defines a special `Null` constant to represent an empty value. This constant is
+	/// convertible to many value types including primitive types `double`, `int` and `int64`
+	/// (defined as lowest number the type can represent). If type supports ordering (<, >),
+	/// all values of the type are greater than Null value. To test whether a value is empty,
+	/// use `IsNull` function.
+
+	int x = Null;
+	int y = 120;
+	Date d = Null;
+	Date e = GetSysDate();
+
+	DUMP(x);
+	DUMP(y);
+	DUMP(d);
+	DUMP(e > d);
+
+	/// Null is the only instance of `Nuller` type. Assigning `Null` to
+	/// primitive types is achieved by cast operators of `Nuller`, other types can do it using
+	/// constructor from `Nuller`.
+	
+	/// As a special case, if Value contains Null, it is convertible to any value type that can contain Null:
+
+	Value v = x; // x is int
+	e = v; // e is Date, but v is Null, so Null is assigned to e
+
+	DUMP(IsNull(e));
+
+	/// Function `Nvl` is U++ analog of well known SQL function coalesce (ifnull, Nvl), which
+	/// returns the first non-null argument (or `Null` if all are `Null`).
+
+	int a = Null;
+	int b = 123;
+	int c = 1;
+
+	DUMP(Nvl(a, b, c));
+	
+	///
+}