Pattern Matching C# with 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(""); 
break; 
} 
} 
is expression 
Pattern matching extends the is operator to check for a type and declare a new variable at the same time. 
Example 
Version < 7.0 
string s = o as string; 
if(s != null) 
{ 
// do something with s 
} 
 

can be rewritten as: 
Version ≥ 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