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I am learning about GUID in C#. While reading, I have come across these two things such as 

1. Guid obj = new Guid();
2. Guid obj = Guid.NewGuid();

I read, the first one always be 16 byte with all 0. The second one will makes an actual GUID with a unique value. Then What is the actual purpose of new Guid();? And When to use it?

thevan
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    http://stackoverflow.com/questions/11938151/guid-newguid-vs-new-guid This is repeated. – CıPhEr Apr 18 '14 at 07:47
  • Then When to use new Guid();? Can anyone place the answer for this? – thevan Apr 18 '14 at 07:52
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    `Guid()` is a default constructor, since it is not taking any parameters, it will give default value which is `Guid.Empty`. – Bharadwaj Apr 18 '14 at 07:54
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    @thevan From [Jon Hanna answer](http://stackoverflow.com/a/11938280/447156): In all, `new Guid()` isn't that useful due to this lack of clarity, **but it's not possible to have a value-type that doesn't have a parameterless constructor that returns an all-zeros-and-nulls value**. – Soner Gönül Apr 18 '14 at 07:54

4 Answers4

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Guid is a value type. The compiler accepts new T() for all value types T, with exactly the same meaning as default(T). A value type cannot prevent this even if default(T) is a nonsensical value for this specific type.

So, to answer your question, new Guid() isn't allowed because it's useful, it's allowed for technical reasons only. You shouldn't ever use it. If you really want an all-zero Guid, default(Guid) or Guid.Empty are far better for readability.

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Then What is the actual purpose of new Guid();?

new Guid() willbe used to intialise the Guid object by calling the constructor.

there is a static method NewGuid() in GUID structure which will return you the actual GUID by calling Guid.NewGuid()

Sudhakar Tillapudi
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I guess the purpose is NOT the parameterless constructor, but the constructor overloads taking an existing GUID.

There are also several cases where you need a parameterless constructor like for deserialization.

Christoph Fink
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You can have a look at GUID implementation here:

http://referencesource.microsoft.com/#mscorlib/system/guid.cs#b622ef5f6b76c10a

Like already said, it is structural type and needs to have default value.

Andrew
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