Guide to the Language

 Struct Field Initializers
Fields within a struct cannot be given initial values, unless they are 
declared as const or static.
struct Point
{
public int x = 1, y = 1; // compile-time error
public static int myStatic = 5; // allowed
public const int myConst = 10; // allowed
}
 Struct Inheritance
A struct cannot inherit from another struct or class, and it cannot be a 
base class. This also means that struct members cannot be declared as 
protected, private protected, or protected internal, and that struct 
methods cannot be marked as virtual. Structs implicitly inherit from 
System.ValueType, which in turn inherits from System.Object. Although 
structs do not support user-defined inheritance, they can implement 
interfaces in the same way as classes.
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 Struct Guideline
The struct type is typically used to represent lightweight classes that 
encapsulate small groups of related variables. The primary reason for 
using a struct instead of a class is to get value type semantics. For 
example, the simple types are in fact all struct types. For these types, it is 
more natural that assignment copies the value rather than the reference.
Structs can also be useful for performance reasons. A struct is 
more efficient than a class in terms of memory. It not only takes up less 
memory than a class, but it also does not need memory to be allocated 
for it as required by reference type objects. Furthermore, a class requires 
two memory spaces, one for the variable and one for the object, whereas 
a struct only needs one. This can make a significant difference for a 
program that operates on a great number of data structures. Bear in 
mind that assignment and parameter passing by value are typically more 
expensive with structs than with reference types, because the entire 
struct needs to be copied for such operations.
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© Mikael Olsson 2020 
M. Olsson, C# 8 Quick Syntax Reference, 
https://doi.org/10.1007/978-1-4842-5577-3_25