Compare with default or empty?

Question

What is the right checking:

Guid value;
// ...
if (value != Guid.Empty)

or

if (value != default(Guid))

I think the 2nd but can't explain why.

Answer 1

Since Guid.Empty == default(Guid) it does not really matter, but I would prefer Guid.Empty for readability.

Answer 2

Guid.Empty is equivalent to new Guid(), which is also equivalent to default(Guid).

When you decompile Guid structure, it seems;

public static readonly Guid Empty = new Guid();

---

Since Guid is a struct, from Default Values Table;

The value produced by setting all value-type fields to their default values and all reference-type fields to null.

Since field types of Guid are, short, int, byte, (and this types default value is 0), when we use default(Guid) we get a Guid with all fields are 0.

From Guid.Empty Field

A read-only instance of the Guid structure whose value is all zeros.

When we write this code;

Console.WriteLine(default(Guid));
Console.WriteLine(new Guid());

outputs;

00000000-0000-0000-0000-000000000000
00000000-0000-0000-0000-000000000000

If you care about readability (which I think you should) Guid.Empty seems better to me.

Answer 3

The both are the same!

Guid.Empty is a readonly field of Guid, having the value {00000000-0000-0000-0000-000000000000}.

With default(Guid) the compile creates a constant value, having {00000000-0000-0000-0000-000000000000}.

In both cases your value is compared to another value somewhere in memory.

Use Guid.Empty for readability.
Use default(T) when you are working with generics.

Answer 4

I would say the second purely because you have the record in an uninitialized state, therefore, it will contain the default value. You are checking whether the variable is in a default state, not whether it's empty - 2 different checks (IMO).

Guid.Empty is the equivalent to default(Guid) in .NET so from a technical point of view it doesn't matter, however, comparing to Guid.Empty gives me the impression that your checking for a particular value, not whether the record is in a default state.