Struct within struct C#

Question

While studying C# , I came across the following piece of code:

public struct position
{
    public static readonly position Zero;
    public double x;
    public double y;
    ...
}

It's not the whole code, but this is the part I need help understanding. Wouldn't creating a instance of the struct inside the struct create a infinite loop?

The key here is static. Leave that out and yes, it would be a problem, and the compiler would complain. But a static is, storage-wise, part of the class, not the instance. — Jeroen Mostert
– Jeroen Mostert, Commented Sep 28, 2022 at 15:04
Consider int.MaxValue or DateTime.Now. They're both members of structs and they both have the same type as the struct. But neither of them will cause a cycle because one is a constant and the other is a static member and they're both accessed via the type name itself, not via an instance. — 41686d6564
– 41686d6564, Commented Sep 28, 2022 at 15:12

Heinzi · Accepted Answer · 2022-09-28 16:57:21Z

5

Wouldn't creating a instance of the struct inside the struct create a infinite loop?

Indeed, and if you remove the static keyword, you actually get the following error message:

Struct member 'position.Zero' of type 'position' causes a cycle in the struct layout

So, why does static "fix" the problem? Because static members are not stored per instance of the struct. Instead, static members are something akin to a "global variable" in C#.

Thus, in your example,

a position is defined by its x, y, etc. values. These are the values that "take up space" when you declare a new instance of your struct.
In addition, there is a special "constant" postition.zero, containing a position with all its values set to the default value. (I put "constant" in quotes, since it's technically not a C# constant, but it behaves similarly to one, since it's readonly.)

edited Sep 28, 2022 at 16:57

answered Sep 28, 2022 at 15:11

Heinzi

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2 Comments

Jeroen Mostert Over a year ago

"Syntactic sugar" is a fairly specific term, and so is "global variable". A static member is "somewhat like" a global variable in other languages, but there is no syntactic sugar involved -- there is no different or more elaborate way to write static declarations.

Heinzi Over a year ago

@JeroenMostert: You are right, it's not "syntactic sugar". I have rephrased it.

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