Diferences between object instantiation in C#: storing objects in references vs. calling a method directly

Question

I have a doubt with the objects declarations in c#. I explain with this example I can do this:

MyObject obj = New MyObject(); 
int a = obj.getInt();

Or I can do this

int a = new MyObject().getInt();

The result are the same, but, exists any diferences between this declarations? (without the syntax)

Thanks.

There is no difference other than the second example doesn't leave a reference to the `MyObject` instance so it will immediately become eligible for GC. — Adam Houldsworth, May 07 '14 at 10:38
If you don't need an instance you should consider to make a method `static`. — Tim Schmelter, May 07 '14 at 10:44
I've edited question's title so it fits better what OP is asking :) — Matías Fidemraizer, May 07 '14 at 10:50

Matías Fidemraizer · Accepted Answer · 2014-05-07T10:44:04.557

4

This isn't a declararation: it's a class instantiation.

There's no practical difference: it's all about readability and your own coding style.

I would add that there're few cases where you will need to declare reference to some object: when these objects are IDisposable.

For example:

// WRONG! Underlying stream may still be locked after reading to the end....
new StreamReader(...).ReadToEnd(); 

// OK! Store the whole instance in a reference so you can dispose it when you 
// don't need it anymore.
using(StreamReader r = new StreamReader(...))
{

} // This will call r.Dispose() automatically

As some comment has added, there're a lot of edge cases where instantiating a class and storing the object in a reference (a variable) will be better/optimal, but about your simple sample, I believe the difference isn't enough and it's still a coding style/readability issue.

edited May 07 '14 at 10:44

answered May 07 '14 at 10:38

Matías Fidemraizer

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_"There's no practical difference"_ there's a great difference if the constructor is _expensive_ and you instantiate them in a loop. – Tim Schmelter May 07 '14 at 10:43
@TimSchmelter Well, we can make my post a wiki article and document every edge case hahaha. I believe your comment makes my answer richer for the OP. Thank you. – Matías Fidemraizer May 07 '14 at 10:45
Thank you Matías, it's a very useful your explanation. – amelian May 07 '14 at 10:59
@AMGHoshi BTW some suggestion. Usually in SO the way to say "thank you" is upvoting every answer you found useful, and choosing one as the best fit to your own question. – Matías Fidemraizer May 07 '14 at 11:28
1

@AMGHoshi Imagine there're 20 answers, you would be adding 20 comments!!! It's easier to upvote every answer and you save time. – Matías Fidemraizer May 07 '14 at 11:28

score 3 · Answer 2 · answered May 07 '14 at 10:38

3

It's mostly syntax.

The main difference is that you can't use the instance of MyObject in the second example. Also, it may be nominated for Garbage Collection immediately.

answered May 07 '14 at 10:38

MarkO

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Can you e xplain to me what is in this case de GC?? – amelian May 07 '14 at 10:48
@AMGHoshi Short answer: GC is the Garbage Collection. Instances of objects no longer referenced in code will be deleted from memory by the GC process. This *may* happen immediately, but most likely at an indeterminate moment in the future. Long answer: See MSDN. – MarkO May 07 '14 at 10:56

score 1 · Answer 3 · answered May 07 '14 at 10:37

No, technically they are the same.

The only thing I would suggest to consider in this case, as if the function does not actual need of instance creation, you may consider declare it static, so you can simply call it like:

int a = MyObject.getInt();

but this naturally depends on concrete implementation.

Diferences between object instantiation in C#: storing objects in references vs. calling a method directly

3 Answers3