var m = new Math();
m.Calc();

class Math{
    public Math(){

    }
    public void Calc(){
        List<string> col = new List<string> {"red","blue","yellow"};

        var y = col.Select(x => {
            Write(x); // Selectは遅延実行なので、Write(x)は書いただけでは呼ばれない
            return x;
        });
    }

    public void Write(string msg){
       Console.WriteLine(msg);
    }
    
}