c# - delegate covariance and Contavariance -

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consider following code snippet

namespace consoleapplication1 {  public delegate tresult function<in t, out tresult>(t args);   class program  {       static void main(string[] args)     {         program pg =new program();         function<object, derivedclass> fn1 = null;         function<string, baseclass> fn2 = null;         fn1 = new function<object, derivedclass>(pg.mycheckfuntion)         fn2=fn1;         fn2("");// calls mycheckfuntion(object a)         pg.mycheckfuntion("hello"); //calls mycheckfuntion(string a)      }       public derivedclass mycheckfuntion(object a)     {         return  new derivedclass();     }     public derivedclass mycheckfuntion(string a)     {          return new derivedclass();     }  }

why delegate call , normal method invocation call different methods.

the delegate bound mycheckfuntion(object) @ compile time - you're telling find method accepts object. binding single method - doesn't perform overload resolution @ execution time based on actual argument type.

when call pg.mycheckfuntion("hello") that bind mycheckfuntion(string) @ compile-time because "hello" string, , conversion string string preferred on conversion string object in overload resolution.

note if write:

object text = "hello"; pg.mycheckfuntion(text);

then that call mycheckfuntion(object).


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