Why are mutable structs evil

But more important than that, you should be able to convince yourself that it does what it does correctly. When objects can change independently across different code "domains", it sometimes becomes difficult to keep track of what is where and why "spooky action at a distance". This is a more difficult concept to exemplify, but it's something that is often faced in larger, more complex architectures. Finally, mutable objects are killer in concurrent situations. Whenever you access a mutable object from separate threads, you have to deal with locking.

This reduces throughput and makes your code dramatically more difficult to maintain. A sufficiently complicated system blows this problem so far out of proportion that it becomes nearly impossible to maintain even for concurrency experts. Immutable objects and more particularly, immutable collections avoid all of these problems. Once you get your mind around how they work, your code will develop into something which is easier to read, easier to maintain and less likely to fail in odd and unpredictable ways.

Immutable objects are even easier to test, due not only to their easy mockability, but also the code patterns they tend to enforce. In short, they're good practice all around! With that said, I'm hardly a zealot in this matter. Some problems just don't model nicely when everything is immutable. In short: the advantages depend somewhat on your problem, but I would tend to prefer immutability. If you do have to use explicit locks, document them throughly.

Especially when it comes to the order in which you lock objects. Asked 6 Months ago Answers: 5 Viewed 42 times. What's the actual problem with mutability and structs in C? Structs are value types which means they are copied when they are passed around. This has nothing to do with Python; global variables are bad in any programming language. If you want to go deeper and find out why side effects are all about, and many other enlightening things, you should learn Functional Programming: Side effect computer science - Wikipedia Why are side-effects considered evil in functional programming?

There are a few aspects to macros that make them "bad" I'll expand on each later, and suggest alternatives : You can not debug macros. Macro expansion can lead to strange side effects.

Macros have no "namespace", so if you have a macro that clashes with a name used elsewhere, you get macro replacements where you didn't want it, and this usually leads to strange error messages.

Skip to content. Simon R. My game — working Now the key thing to notice is that there are lots of squares on the landscape — which I represent by a class called Square My inventiveness when it comes to imaginative class names amazes me sometimes. AddBuilding BuildingType. TownHouse, Direction. NE ; Looks innocuous enough.

Get the Features on a square tile, and add a building to it. Where are the features? Like this: Like Loading Tagged beaches BlackZephyr C game immutability Programming valuetypes. Published by Simon R. Published February 18, February 18, Add …. Hello, Mr. Hi Simon, interesting read. Any operations which modify the List will then internally modify Square, which is a class.

Good call on being innovative! Thanks for the idea! Sorry for the long delay replying to your suggestion btw. Comment on this article your first comment on TechieSimon will be moderated Cancel reply Enter your comment here Fill in your details below or click an icon to log in:. Email required Address never made public. Name required. Follow Following. Techie Simon Join 25 other followers. Sign me up. Already have a WordPress.

Log in now. Loading Comments Email Required Name Required Website. These simply can't occur in immutable structures, since a write is not a valid operation. Also, I claim that mutability is almost never actually needed , the programmer just thinks that it might be in the future. For example, it simply doesn't make sense to change a date. Rather, create a new date based off the old one.

This is a cheap operation, so performance is not a consideration. Python Javascript Linux Cheat sheet Contact. Nothing useful