CODEWITHSUNDEEP
c#
Eric Yin
Eric Yin

Reputation: 8973

Whats the difference between these three ways of creating a new List<string> in C#?

Whats the difference between these three ways of creating a new List<string> in C#?

A = new List<string>();
B = new List<string> { };
C = new List<string>() { };

Upvotes: 5

Views: 215

Answers (6)

Femaref
Femaref

Reputation: 61437

Those are equivalent, all three create an empty List<string>.

  1. is a simple, parameterless constructor
  2. uses the collection initialization syntax, where you are allowed to omit the braces of the constructor if the class provides a parameterless constructor
  3. the same as 2., just providing the optional constructor braces.

The collection initialization syntax allows you to provide data while constructing the object,

List<string> list = new List<string> { "one", "two", "three" };

gets expanded to

List<string> list = new List<string>();
list.Add("one");
list.Add("two");
list.Add("three");

by the compiler.

Upvotes: 4

Jason Down
Jason Down

Reputation: 22161

There is no difference because you are not initializing anything inside the list at the time of declaring it.

If you were to add some strings at declaration-time, you would need to go with the second or third choice:

var B = new List<string> { "some", "strings" };
var C = new List<string>() { "some", "strings" };

The third option would only be necessary if you were to pass a value into the List<of T> constructor:

var C = new List<string>(5) { "some", "strings" };

or

var C = new List<string>(5); // empty list but capacity initialized with 5.

There are more constructors available for the List<of T> class as well (e.g. passing an existing collection or IEnumerable into the List constructor). See MSDN for details.

Upvotes: 8

Bruno Costa
Bruno Costa

Reputation: 2720

In the example you gave to us, the result will be the same.

In terms of performance you will not find any problem using any of that options for initializing a empty list, because the IL generated will one contain the ctor(), as you can see using the IL DASM.

If you want to initialize the list with some information, you can go for the option 2 or 3.

List<string> b = new List<string> { "abc", "abc" };
List<string> c = new List<string>() { "abc", "abc"};

In terms of performance is also the same, the IL generated will be exactly the same, containing the ctor() and two Add for both.

But you should use the best one to read. To avoid any problem reading the code for you colleagues, I would go for 

 List<string> a = new List<string>();

But that is a question of personal opinion.

Upvotes: 1

gdoron
gdoron

Reputation: 150253

{} is used for collection\object initilizer.
If it remains blank it doesn't do a thing.

So all those lines produces the same thing.

Upvotes: 1

Yogu
Yogu

Reputation: 9445

In your example, all three statements do the same: they create an empty string list. Statement B and C can assign some initial data to the list, e.g.

ingredients = new List<string> { "Milk", "Sugar", "Flour" };

The () as in statement C can omitted then.

Upvotes: 1

Gabe
Gabe

Reputation: 86708

Those are all identical. There's no difference in the end result, just in the syntax.

Upvotes: 4

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