Is there a difference between select new T() and select new T in LINQ

Question

I've been experimenting today with LINQ and DataTable today.

var query = from row1 in table1.AsEnumerable()
            from row2 in table2.AsEnumerable()
            where
            (row1.Field<string>("a") == row2.Field<string>("b"))

            select new Foo
               {
                   Property1 = row1.Field<string>("Hey")
                   Property2 = row2.Field<string>("Ho")
               };

and came to strange conclusion that regardless if I do select new Foo or select new Foo() the query worked exactly the same. I would really like to go into more depth of linq mechanics with delegates etc. to understand this clearly - but for now, for a simple man - is there a difference, and if so, what would this be?

Edit The question has already some similar answers here on SOF, but "object initializer" does not come on top of mind. It is also raised quite specific to LINQ, where 90% of web hints operate on anonymous types(not sure why, I found some good benefit of using concrete types, especially Intellisense). If any materials do specify concrete type implementation example in LINQ I was only able to find new Foo without parentheses . With LINQ construction especially for beginners it might be tricky to find out what is initialized there (object, delegate, predicate etc. - at least it was for me) so hopefully at least some people will find the question and responses useful.

both great answers. Thank you, I'm really having a hard time to decide which one to accept - 1 faster, or 2nd the examples from John Skeet really speak to me. — Turo, Dec 30 '15 at 22:19
Can I ask a small clarifying question - I somehow don't get intellisense for e.g. Property1 within the query ? this would be normal? — Turo, Dec 30 '15 at 22:21
IntelliSense should work the same if you have the parentheses or not... maybe just your IDE is being slow? — Frank Bryce, Dec 30 '15 at 22:22
Thank you John, Intellisense works, which is great! @Jakub - no offense and thank you for your answer as well, I somehow could not resist John Skeet ;) — Turo, Dec 30 '15 at 22:25
Possible duplicate of [difference between initializing an object with these two ways in c#](http://stackoverflow.com/questions/17105618/difference-between-initializing-an-object-with-these-two-ways-in-c-sharp) — Vadim Martynov, Dec 30 '15 at 23:12

score 10 · Accepted Answer · edited May 23 '17 at 11:59

These two expressions are exactly the same in C#

new Foo
{
    Property1 = row1.Field<string>("Hey")
    Property2 = row2.Field<string>("Ho")
};

and

new Foo()
{
    Property1 = row1.Field<string>("Hey")
    Property2 = row2.Field<string>("Ho")
};

because Jon said so, and Mr. Lippert tells us why the C# gods chose to make it so in C# 3.0

In your larger example, the select takes an expression of this form, and since the object initializer expression is the same then the larger expression also yields the same result :)

score 6 · Answer 2 · answered Dec 30 '15 at 22:13

If you use an object initializer and don't pass any parameters to the constructor, the parenthesis can be omitted. Both statements are equivalent.

From C# language specification:

An object creation expression can omit the constructor argument list and enclosing parentheses provided it includes an object initializer or collection initializer. Omitting the constructor argument list and enclosing parentheses is equivalent to specifying an empty argument list.

Is there a difference between select new T() and select new T in LINQ

2 Answers2