Diffrents usage of ! operator

Question

can someone explain to me the diffrence between default and default!

for example:

public string FirstName { get; set; } = default!;

to:

public string FirstName { get; set; } = default;

`!` is *null forgiving operator*, so you assign `default` value (which is `null` in case of `string`) and do not want to get warning for this: note that `FirstName` is of type `string`, not `string?`. — Dmitry Bychenko, Dec 13 '22 at 11:20
From an IL-perspective both statements are identical. The null-forgiving operator is just an indicator for the compiler to **not** throw a warning if you attempt to assign `null` to a non-nullable reference-type — MakePeaceGreatAgain, Dec 13 '22 at 11:24

score 4 · Accepted Answer · answered Dec 13 '22 at 11:28

Well, ! is a null forgiving operator. In your case you assign default value (which is null in case of string) to string property and don't want to get warning:

 // FirstName should not be null
 // but you assign default (null) value to it
 // and don't want to get warning about it (you know what you are doing)
 public string FirstName { get; set; } = default!;

Another possibility is to allow null (note string? instead of string):

 // FirstName can be null
 // We assign default (null) value to it
 public string? FirstName { get; set; } = default;

In case of

 // FirstName is not suppose to be null
 // But we assign default (which is null)
 // Compiler can warn you about it
 public string FirstName { get; set; } = default;

Diffrents usage of ! operator

1 Answers1