D - Contract Programming

Contract programming in D programming is focused on providing a simple and understandable means of error handpng. Contract programming in D are implemented by three types of code blocks −

body block

in block

out block

Body Block in D

Body block contains the actual functionapty code of execution. The in and out blocks are optional while the body block is mandatory. A simple syntax is shown below.

return_type function_name(function_params) 
in { 
   // in block 
} 

out (result) { 
   // in block 
}
 
body { 
   // actual function block 
}

In Block for Pre Conditions in D

In block is for simple pre conditions that verify whether the input parameters are acceptable and in range that can be handled by the code. A benefit of an in block is that all of the entry conditions can be kept together and separate from the actual body of the function. A simple precondition for vapdating password for its minimum length is shown below.

import std.stdio; 
import std.string;
  
bool isVapd(string password) 
in { 
   assert(password.length>=5); 
}
 
body { 
   // other conditions 
   return true; 
}
  
void main() { 
   writeln(isVapd("password")); 
}

true 

import std.stdio;
import std.string;

double getAge(double months,double years) 
in { 
   assert(months >= 0); 
   assert(months <= 12); 
}
 
out (result) { 
   assert(result>=years); 
} 

body { 
   return years + months/12; 
} 
 
void main () { 
   writeln(getAge(10,12)); 
} 

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