使用可为空的结构能否提高性能？

Question

I was thinking the following:

Since, structs can improve GC performance and Nullable<T> is a struct itself, would it be better in terms of performance (GC performance or overall) to use a nullable struct instead of a class?

Has anyone experience on this?

EDIT:

Eg: I was thinking more about creating an options class/struct for a method call: ConvertToPdf(..., MyType options) . So, not extra huge structs with many methods or anything like that.

Answer 1

No.

structs .. being the basis for value types, should remain small. Classes don't generally remain small, and so by substituting all uses of a class for a struct .. you will be creating in fact slower runtime speeds.. since value types are copied in their entirety.

Answer 2

A structure is semantically equivalent to a bunch of variables stuck together with duct tape. If one were to create a structure

public struct MaybeValid<T>
{
  public T Value;
  public bool IsValid;
}

then the Value field of a variable of a MaybeValid<T> could be worked with just as efficiently as a variable of type T . The Framework's Nullable<T> isn't defined that way, however. Consequently, it's often necessary to copy the Value of a Nullable<T> to some other variable before anything can be done with it. The extra layers of copying required when using Nullable<T> mean that code using it will generally be nowhere near as efficient as code using other types could be.

Answer 3

Premature optomisation! - given that possible as you don't get boxing directly as you would wrapping it in a class you can make nullable. Assuming of course that use of a struct is appropriate - you do tend to see a lot of classes with very few members, these could be a target. But you dont want to optomize like this until you know you need to because you are only a mortal.