How to make a 'struct' Nullable by definition?

Question

struct AccountInfo { String Username; String Password; }

now if I want to have a Nullable instance I should write:

Nullable<AccountInfo> myAccount = null;

But I want make the struct Nullable by nature and it can be used like this (without use of Nullable<T>):

AccountInfo myAccount = null;

I was thinking with just two members, it would be a funny class I was ashamed someone look into my code :) — Xaqron
– Xaqron, Commented Dec 20, 2010 at 17:03
A mutable structure is much more problematic than a class with only two members. — Dan Bryant
– Dan Bryant, Commented Dec 20, 2010 at 17:39
Side comment: any reason on using String instead of string? — danielrozo
– danielrozo, Commented Feb 6, 2014 at 13:02
The answers that say "make it a class," while fundamentally correct, don't account for the case where you are using a third party library that contains a struct type. In some cases, you may want a data member of that type that can be uninitialized or unset, and there's no obvious default value that works. Edit: Which ziplin's solution below DOES address. — Tim Keating
– Tim Keating, Commented Apr 28, 2015 at 20:34

Community · Accepted Answer · 2017-05-23 11:47:23Z

You can't. Struct are considered value types, and by definition can't be null. The easiest way to make it nullable is to make it a reference type.

The answer you need to ask yourself is "Why is this a struct?" and unless you can think of a really solid reason, don't, and make it a class. The argument about a struct being "faster", is really overblown, as structs aren't necessarily created on the stack (you shouldn't rely on this), and speed "gained" varies on a case by case basis.

See the post by Eric Lippert on the class vs. struct debate and speed.

Dlongnecker · Accepted Answer · 2018-07-04 14:56:48Z

58

When you declare it, declare it with a "?" if you prefer

AccountInfo? myAccount = null;

edited Jul 4, 2018 at 14:56

user142162

answered Dec 20, 2010 at 16:57

Dlongnecker

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2 Comments

Chris Farmer Over a year ago

That's not "defining" it. That's declaring it.

KitChaos Over a year ago

Adding ? after my variable dec at the top of my file worked for me, let it be null. I personally like structs when I need collections of datasets, especially for unity where dictionaries dont show up in the inspector. Thanks for answering the question and not just saying "Lul you are doing it wrong go learn harder"

Greg Beech · Accepted Answer · 2010-12-20 17:01:18Z

The short answer: Make it a class.

The long answer: This structure is mutable which structs should never be, doesn't represent a single value which structs always should, and has no sensible 'zero' value which structs also always should, so it probably shouldn't be a value type. Making it a class (reference type) means that it is always possible for it to be null.

Note: Use of words such as "never" and "always" should be taken with an implied "almost".

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