循环中的性能差异[重复]

可能重复:
Difference between declaring variables before or in loop?

当我编写类似这样的示例时,是否存在任何(或任何显著的)性能差异(考虑从DB将数十行或数十万行加载到Foo对象集合中):

...
Foo myFoo;

while(reader.Read())
{
    myFoo = new Foo();
    myFoo.SomeProperty = reader.GetValue(0);
    ...
    fooCollection.Add(myFoo);
}

...

while(reader.Read())
{
    Foo myFoo = new Foo();
    myFoo.SomeProperty = reader.GetValue(0);
    ...
    fooCollection.Add(myFoo);
}