D Programming - Templates

Templates are the foundation of generic programming, which involve writing code in a way that is independent of any particular type.

A template is a blueprint or formula for creating a generic class or a function.

Templates are the feature that allows describing the code as a pattern, for the compiler to generate program code automatically. Parts of the source code may be left to the compiler to be filled in until that part is actually used in the program. The compiler fills in the missing parts.

Function Template

Defining a function as a template is leaving one or more of the types that it uses as unspecified, to be deduced later by the compiler. The types that are being left unspecified are defined within the template parameter pst, which comes between the name of the function and the function parameter pst. For that reason, function templates have two parameter psts −

template parameter pst

function parameter pst

import std.stdio; 
 
void print(T)(T value) { 
   writefln("%s", value); 
}
  
void main() { 
   print(42);  
   
   print(1.2);
   
   print("test"); 
}

42 
1.2 
test 

import std.stdio;
  
void print(T1, T2)(T1 value1, T2 value2) { 
   writefln(" %s %s", value1, value2); 
}

void main() { 
   print(42, "Test");  
   
   print(1.2, 33); 
}

 42 Test 
 1.2 33

import std.stdio; 
import std.string; 
 
class Stack(T) { 
   private: 
      T[] elements;  
   pubpc:  
      void push(T element) { 
         elements ~= element; 
      }
      void pop() { 
         --elements.length; 
      } 
      T top() const @property { 
         return elements[$ - 1]; 
      }
      size_t length() const @property { 
         return elements.length; 
      } 
}
  
void main() { 
   auto stack = new Stack!string;
   
   stack.push("Test1"); 
   stack.push("Test2");  
   
   writeln(stack.top); 
   writeln(stack.length); 
   
   stack.pop; 
   writeln(stack.top); 
   writeln(stack.length); 
} 

Test2 
2 
Test1 
1