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Removing a singleton is incredibly costly due to the "close coupling, global state, multiple responsibility, and dependency hiding that are enabled by it". If

Removing a singleton is incredibly costly due to the "close coupling, global state, multiple responsibility, and dependency hiding that are enabled by it". If I were to compile a top 10 list of terrible refactoring projects I've worked on, ALL of them would be on code that had stalled out due to a "singleton" global variable code-complexity ceiling. Anti-singleton is a holy war because the people who produce such shockingly crap singleton-riddled code are externalizing enormous and soul-crushing costs onto both customers and future maintainers.

logfromblammo 12y ago
I guess we know which side you're on, then. I'd caution against inverting the conditional probability of writes singletons given unskilled programmer into probability of unskilled programmer given writes singletons. It's a fallacious operation. You can't eliminate bad code by eliminating singletons. You can only do it by turning unskilled programmers into skilled programmers. "Don't use singletons" is fine advice for a novice, but it would be better to teach the principles that underlie that advice and use Socratic questioning to make them realize that MOST uses of singleton violate one or more of those principles.
- perdunov 12y ago
  You're right that writing singletons needs expertise because there are a number of (possibly unsolvable) gotchas that you need to know about to even start using singletons. Take the self-referencing problem: let's say we have a logger singleton (pretty simple, what could possibly go wrong?) And let's say that the logger singleton invokes particular code during its initialization, such as the file I/O code that is also our own and that uses... guess what? a logger! Thus, when the logger class initializes, it will either try to log using an uninitialized object or invoke the initialization recursively depending on whether the singleton is lazy or not. A beginner is normally not aware of this problem when they are writing their singleton class. Another problem is the initialization order: what is initialized first - the logger singleton or the I/O singleton? Turns out, we just have to use lazy initialization. Then the multithreading comes on the scene. So you have to make a thread safe lazy singleton. But that implies additional cost on every call for the singleton. I don't know... Singletons are a mess.
- teacup50 12y ago
  You can eliminate bad programmers by eliminating those that would use global variables.

logfromblammo 12y ago

I guess we know which side you're on, then. I'd caution against inverting the conditional probability of writes singletons given unskilled programmer into probability of unskilled programmer given writes singletons. It's a fallacious operation. You can't eliminate bad code by eliminating singletons. You can only do it by turning unskilled programmers into skilled programmers. "Don't use singletons" is fine advice for a novice, but it would be better to teach the principles that underlie that advice and use Socratic questioning to make them realize that MOST uses of singleton violate one or more of those principles.

perdunov 12y ago
You're right that writing singletons needs expertise because there are a number of (possibly unsolvable) gotchas that you need to know about to even start using singletons. Take the self-referencing problem: let's say we have a logger singleton (pretty simple, what could possibly go wrong?) And let's say that the logger singleton invokes particular code during its initialization, such as the file I/O code that is also our own and that uses... guess what? a logger! Thus, when the logger class initializes, it will either try to log using an uninitialized object or invoke the initialization recursively depending on whether the singleton is lazy or not. A beginner is normally not aware of this problem when they are writing their singleton class. Another problem is the initialization order: what is initialized first - the logger singleton or the I/O singleton? Turns out, we just have to use lazy initialization. Then the multithreading comes on the scene. So you have to make a thread safe lazy singleton. But that implies additional cost on every call for the singleton. I don't know... Singletons are a mess.
teacup50 12y ago
You can eliminate bad programmers by eliminating those that would use global variables.