C# Language C# 7.0 Features Pattern Matching
Example
Pattern matching extensions for C# enable many of the benefits of pattern matching from functional languages, but in a way that smoothly integrates with the feel of the underlying language
switch expression
Pattern matching extends the switch statement to switch on types:
class Geometry {}
class Triangle : Geometry
{
public int Width { get; set; }
public int Height { get; set; }
public int Base { get; set; }
}
class Rectangle : Geometry
{
public int Width { get; set; }
public int Height { get; set; }
}
class Square : Geometry
{
public int Width { get; set; }
}
public static void PatternMatching()
{
Geometry g = new Square { Width = 5 };
switch (g)
{
case Triangle t:
Console.WriteLine($"{t.Width} {t.Height} {t.Base}");
break;
case Rectangle sq when sq.Width == sq.Height:
Console.WriteLine($"Square rectangle: {sq.Width} {sq.Height}");
break;
case Rectangle r:
Console.WriteLine($"{r.Width} {r.Height}");
break;
case Square s:
Console.WriteLine($"{s.Width}");
break;
default:
Console.WriteLine("<other>");
break;
}
}
is expression
Pattern matching extends the is operator to check for a type and declare a new variable at the same time.
Example
7.0
string s = o as string;
if(s != null)
{
// do something with s
}
can be rewritten as:
7.0
if(o is string s)
{
//Do something with s
};
Also note that the scope of the pattern variable s is extended to outside the if block reaching the end of the enclosing scope, example:
if(someCondition)
{
if(o is string s)
{
//Do something with s
}
else
{
// s is unassigned here, but accessible
}
// s is unassigned here, but accessible
}
// s is not accessible here
