I know what you are saying, and agree. But consider: I have state that I truly need to be global - something I read from an INI file, the command line, or internally calculated, it doesn't much matter. Is not the alternative to a singleton having that state replicated all over the place? And then you introduce model/view/ signals, have to deal perhaps with race conditions, and so on. Then, just try to grep for the existence of that state in your code.
Like anything, it's a tradeoff. Let's say I have an app with 10 OpenGL windows, and I want to simultaneously control the lighting model for all at once. A singleton gives me an easy way to do that, but then the windows have to poll in some manner (which is perhaps not an issue, since they are in a render loop anyway). But I am brittle - introduce the requirement that each window handles light differently and the singleton is toast. OTOH, introducing a signal/slot or model/view architecture may be overkill for what I am doing. This might be a small corner of the code, and I just want clarity for the few times I go in to read it. I find it extraordinarily hard to understand messaging code - where did this message come from, what was the state of that object that caused it to fire the message, and so on. I think complexity goes up at least by 1 order of magnitude when you have to maintain state and time in your mind to understand a program.
Perhaps not the best example; so consider command line arguments. It's read only, set once, but perhaps needed to be accessed by many different parts of my code. A singleton or 5 seems pretty darn clean to me. Again, not without it's tradeoffs, but the alternatives, to me, seem worse. You can pass, pass, pass, the data through methods and constructors until it gets to the code that needs the info - in which case you have infected a lot of code with rather superfluous (to them) knowledge about command line settings. That's brittle, and you end up touching a lot of code when you add something to the command line. You can do a signal/slot or model/view, which can be quite powerful, but you may be forced into a specific design by your sw stack (they have a model/view architecture which you are using for GUI or something). So your code is brittle by being coded to a specific API, and again, it rather obscures where this data comes from. Plus, this forces the command line reading code to know all about your specific API, how to format the signal, when to send it (command line reading is often done well before the whole stack is started up and going, so you can't send a signal yet). That's very brittle as well. Can you take that code, put it in a test harness, and trivially write tests for it? Probably not.
Maybe I am missing some obvious technique. But a few things in an app are in fact global. Trying to obscure that fact, to my mind, just makes the sw more brittle and a lot harder to understand and debug. Which is not in any way an argument for making non-global things global for convenience.
I think you really hit the core issue here with singletons. There is no problem with global state if it is truly immutable (at least after initialization).
But the majority of singletons I have seen in practice (maybe my bad luck) contain mutable state. In the almost two decades I have been programming I have never come across a situation where I needed a singleton with mutable state. But hey I have not seen it all.
Sure, but for the most part, there is no reason for the components of the app to depend on those things being global (and a significant cost in brittleness for them to do so), so, in general, they should be passed to the objects that need them, even if they are globally consistent throughout the app.
Obviously, there are optimization reasons why you might need to avoid doing this in particular cases, but in general doing so up-front is going to be a premature optimization.
"...there is no reason for the components of the app to depend on those things being global..."
BINGO! This is the anti-pattern part. Not that the data is globally required, but that your units are mutually dependable. This is why Interfaces and Dependency Injection are so popular now, because they facilitate the ability to make easily testable, singular units that allow for mocks / stubs etc.
To illustrate, what happens if your global requirement happens to also be external? Would you want to have to test your component with a live version of your global and external resource? No, you would want the ability to test (either as a single unit, or even the whole app), without requiring the database, messaging, web service, etc, to be up.
One of the links in the original article, actually points to a StackExchange answer specifically commenting on the difference between single instance and singleton. It's a great read.
http://programmers.stackexchange.com/a/40610/42446
Like anything, it's a tradeoff. Let's say I have an app with 10 OpenGL windows, and I want to simultaneously control the lighting model for all at once. A singleton gives me an easy way to do that, but then the windows have to poll in some manner (which is perhaps not an issue, since they are in a render loop anyway). But I am brittle - introduce the requirement that each window handles light differently and the singleton is toast. OTOH, introducing a signal/slot or model/view architecture may be overkill for what I am doing. This might be a small corner of the code, and I just want clarity for the few times I go in to read it. I find it extraordinarily hard to understand messaging code - where did this message come from, what was the state of that object that caused it to fire the message, and so on. I think complexity goes up at least by 1 order of magnitude when you have to maintain state and time in your mind to understand a program.
Perhaps not the best example; so consider command line arguments. It's read only, set once, but perhaps needed to be accessed by many different parts of my code. A singleton or 5 seems pretty darn clean to me. Again, not without it's tradeoffs, but the alternatives, to me, seem worse. You can pass, pass, pass, the data through methods and constructors until it gets to the code that needs the info - in which case you have infected a lot of code with rather superfluous (to them) knowledge about command line settings. That's brittle, and you end up touching a lot of code when you add something to the command line. You can do a signal/slot or model/view, which can be quite powerful, but you may be forced into a specific design by your sw stack (they have a model/view architecture which you are using for GUI or something). So your code is brittle by being coded to a specific API, and again, it rather obscures where this data comes from. Plus, this forces the command line reading code to know all about your specific API, how to format the signal, when to send it (command line reading is often done well before the whole stack is started up and going, so you can't send a signal yet). That's very brittle as well. Can you take that code, put it in a test harness, and trivially write tests for it? Probably not.
Maybe I am missing some obvious technique. But a few things in an app are in fact global. Trying to obscure that fact, to my mind, just makes the sw more brittle and a lot harder to understand and debug. Which is not in any way an argument for making non-global things global for convenience.