Comments on: Why Are Mutable Value Types Even Possible?

By: Daniel Earwicker

Daniel Earwicker — Mon, 18 May 2009 09:56:48 +0000

Structs seemed like such an irresistable addition (compared to Java) when I first read about them, but they are practically useless. The only places you might need them is in order to create an array of structs for some obscure interop scenarios, or as an optimisation technique (but ONLY after profiling reveals abnormally high pressure on the GC).

In terms of general program design, forget about them. They’re just one problem after another.

If they are needed for those edge-cases, fine, but maybe they should have only worked inside an “unsafe” block! They should have been made as unattractive as possible, to deter people from using them where a class would be fine.

For example, it should have been illegal to define events in a struct. Events signal a state change, and structs ought to be immutable, hence an event on a struct should ring alarm bells.

Also the inability to control how and when they are constructed makes large-scale design very difficult. Any struct can always be constructed with its contents zero-inited, and there’s no way to ban that.

By: Reflective Perspective - Chris Alcock » The Morning Brew #349

Reflective Perspective - Chris Alcock » The Morning Brew #349 — Mon, 18 May 2009 06:57:00 +0000

[...] Why Are Mutable Value Types Even Possible? – Davy Brion explores one of the confusing compiler errors which can be caused by using value types and not realising [...]

By: Davy Brion

Davy Brion — Sun, 17 May 2009 16:48:00 +0000

@Senthil

well, in that case it’s not really so weird because then you have direct access to it, instead of it being passed around as so happens when using a property.

but the fact that the code itself would work when using a field makes the whole thing even more likely to cause confusion

By: Senthil Kumar

Senthil Kumar — Sun, 17 May 2009 16:11:03 +0000

My guess is to make initialization less painful, if the type has a bunch of fields. Although having a large number of fields in a struct is not recommeneded.

That apart, try changing SomePoint to a public field (rather than a property), and the code will compile and work as expected. I’ve always found that a bit weird.