S>public shape SGroup<T>      
S>{      
S> static T operator +(T t1, T t2);      
S> static T Zero {get;}       
S>}  
S>

S>This declaration says that a type can be an SGroup<T> if it implements a+ operator over T, and a Zero static property.

S>public extension IntGroup of int: SGroup<int>    
S>{    
S> public static int Zero => 0;    
S>}   
S>

S>And the extension.

S>public static AddAll<T>(T[] ts) where T: SGroup<T> // shape used as constraint    
S>{    
S> var result = T.Zero; // Making use of the shape's Zero property    
S> foreach (var t in ts) { result += t; } // Making use of the shape's + operator    
S> return result;    
S>}   
S>

S>int[] numbers = { 5, 1, 9, 2, 3, 10, 8, 4, 7, 6 };     
  
S>WriteLine(AddAll(numbers)); // infers T = int   
S>

S> public shape SGroup<T>
S>

S>public extension IntGroup of int: SGroup<int> 
S>

S>role IntGroup  extednds int
S>

S>public static int Zero => 0; 
S>