c# - Conditional Expression Return Type -

i have 2 classes implementing imyinterface , async method of return type task<imyinterface>.

why receiving compiler error "there no implicit conversion type" return statement, return somebooleandeterminedbythemethod ? class1 : new class2(); , best procedure resolving this?

full method:

public static async task<imyinterface> mymethodasync(subclass1 class1child) {     var listofthings = new list<tuple<int, class1>>();     await task.run(() =>     {         foreach (var item in somecollection)         {             var dummyclass1 = new class1() {intproperty = 0};             var computationresult = new tuple<int, class1>( dummyclass1.intproperty, dummyclass1);             listofthings.add(computationresult);         }     }      try      {         var returnedclass1 = (from items in listofthings                           orderby items.item1                           select items.item2).firstordefault();         return returnedclass1.booleanproperty ? returnedclass1 : new class2();     }     catch ... // not relevant. }  class class1 : imyinterface {     public int intproperty { get; set;}     public bool booleanproperty => intproperty % 2 == 1; // so, in example, booleanproperty return false. }  class class2 : imyinterface {     // class serves separate class indicate different type used program.  }  interface imyinterface { }  

as documentation ?: operator explains:

given conditional expression: condition ? first_expression : second_expression;

either type of first_expression , second_expression must same, or implicit conversion must exist 1 type other.

since neither class1 or class2 same type, nor implicit conversion exist between two, can cast either first_expression or second_expression interface type, so:

return somebooleandeterminedbythemethod ? (imyinterface)class1 : new class2(); 

then compiler know expression should evaluate imyinterface.