Question

Are there significant performance differences (at runtime and/or compile time) between constructing and assigning the properties of a class like this:

Employee currentUser = new Employee();
currentUser.Name = "Bob";

or like this:

Employee currentUser = new Employee() { Name = "Bob" };

My actual example is not that simple, the properties of the class are actually assigned to some long linq expressions.

I searched Google and Stack Overflow for answers but i only found questions regarding best practices, when to use either method, and not anything performance related.

Apologies in advance if i’m asking a silly question.

Answer 1

No. This is only a syntactic sugar. The IL generated will be the same (Will be updating with IL)

internal class Foo
{
    public string Bar { get; set; }
}
class Program
{
    static void Main(string[] args)
    {
        Foo f = new Foo()
                    {
                        Bar = "Baaz"
                    };
        Console.WriteLine("Now the old way sugar");
        Foo f2 = new Foo();
        f2.Bar = "Baaz";

    }
}

Now IL:

  IL_0000:  nop
  IL_0001:  newobj     instance void SimpleDataPlayGround.Foo::.ctor()
  IL_0006:  stloc.2
  IL_0007:  ldloc.2
  IL_0008:  ldstr      "Baaz"
  IL_000d:  callvirt   instance void SimpleDataPlayGround.Foo::set_Bar(string)
  IL_0012:  nop
  IL_0013:  ldloc.2
  IL_0014:  stloc.0
  IL_0015:  ldstr      "Now the old way sugar"
  IL_001a:  call       void [mscorlib]System.Console::WriteLine(string)
  IL_001f:  nop
  IL_0020:  newobj     instance void SimpleDataPlayGround.Foo::.ctor()
  IL_0025:  stloc.1
  IL_0026:  ldloc.1
  IL_0027:  ldstr      "Baaz"
  IL_002c:  callvirt   instance void SimpleDataPlayGround.Foo::set_Bar(string)
  IL_0031:  nop
  IL_0032:  ret

---

UPDATE

OK, after comments from Jon, it is obvious that there is a slight difference. But as for the question – mainly performance implications – there is none but as Jon points out, this can be important if an object is used for its own re-creation.