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C++ says “We have try... finally at home”

devblogs.microsoft.com

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Re: C++ says “We have try... finally at home”

#121

Post by locknitpicker »

afiori wrote: post #118
locknitpicker wrote: post #39

Earlier quoted context omitted.

> So some kids would complain that C++ destructors RAII philosophy require creating a whole "class X{public:~X()}" which is sometimes inconvenient so it doesn't exactly equal "finally". Those figurative kids would be stuck in a mental model where they try to shoehorn their ${LanguageA} idioms onto applications written in ${LanguageB}. As the article says, C++ has destructors since the "C with Classes" days. Complaini…

Ok, but sometimes you just need a single line in a finally and writing a class is more annoying

> Ok, but sometimes you just need a single line in a finally and writing a class is more annoying

I don't think you understand.

If you need to run cleanup code whenever you need to destroy a resource, there is already a special member function designed to handle that: the destructor. Read up on RAII.

It somehow you failed to understand RAII and basic resource management, you can still use one-liners. Read up on scope guard.

If you are too lazy to learn about RAII and too lazy to implement a basic scope guard, you can use one of the many scope guard implementations around. Even Boost has those.

https://www.boost.org/doc/libs/latest/libs/scope/doc/html/sc...

So, unless you are lazy and want to keep mindlessly writing Java in ${LANGUAGE} regardless it makes sense or not, there is absolutely no reason at all to use finally in C++.

Re: C++ says “We have try... finally at home”

#122

Post by Someone »

kibwen wrote: post #104
Someone wrote: post #48

Earlier quoted context omitted.

I think Swift’s defer ( https://docs.swift.org/swift-book/documentation/the-swift-pr... ) was inspired by/copied from go ( https://go.dev/tour/flowcontrol/12 ), but they may have taken it from an even earlier language that I’m not aware of. Defer has two advantages over try…finally: firstly, it doesn’t introduce a nesting level. Secondly, if you write foo defer revert_foo , when scanning the code, it’s easier to veri…

I'll disagree here. I'd much rather have a Python-style context manager, even if it introduces a level of indentation, rather than have the sort of munged-up control flow that `defer` introduces.

I can see your point, but that (https://book.pythontips.com/en/latest/context_managers.html) requires the object you’re using to implement __enter__ and __exit__ (or, in C#, implement IDisposable (https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...), in Java, implement AutoCloseable (https://docs.oracle.com/javase/tutorial/essential/exceptions...); there likely are other languages providing something similar).

Defer is more flexible/requires less boilerplate to add callsite specific handling. For an example, see https://news.ycombinator.com/item?id=46410610

Re: C++ says “We have try... finally at home”

#123

Post by actionfromafar »

mort96 wrote: post #91
actionfromafar wrote: post #84

Earlier quoted context omitted.

As someone coming from RAII to C#, you get used to it, I'd say. You "just" have to think differently. Lean into records and immutable objects whenever you can and IDisposable interface ("using") when you can't. It's not perfect but neither is RAII. I'm on a learning path but I'd say I'm more productive in C# than I ever was in C++.

I agree with this. I don't dislike non-RAII languages (even though I do prefer RAII). I was mostly asking a rhetorical question to point out that it really isn't the same at all. As you say, it's not a RAII language, and you have to think differently than when using a RAII language with proper destructors.

Pondering - is there a language similar to C++ (whatever that means, it's huge, but I guess a sprinkle of don't pay for what you don't use and being compiled) which has no raw pointers and such (sacrificing C compatibility) but which is otherwise pretty similar to C++?

Re: C++ says “We have try... finally at home”

#124

Post by zem »

rramadass wrote: post #63
mort96 wrote: post #61

Earlier quoted context omitted.

It has been up with the incorrect title for over 7 hours now. That's most of the Hacker News front-page lifecycle. The system for correcting bad automatic editorialisation clearly isn't working well enough.

Oh, come on man! These are trivial bugs . Whoever noticed it first should have sent the email to the mods. I did it before i posted my previous comment and i now see that the title has been changed appropriately.

it's not a trivial bug, it creates the same sort of aversive reaction that obvious AI slop banner images do.

Re: C++ says “We have try... finally at home”

#125

Post by ibobev »

hyghjiyhu wrote: post #116
ibobev wrote: post #106

Earlier quoted context omitted.

I intentionally shortened the title because there is a length limit. Perhaps I didn't do it the right way because I was unfamiliar with the mentioned meme. Sorry about that.

It's important even without the meme. c++ has try-catch but not try-finally.

It is common for some titles to exceed the allowed length limit on HN. I often do not have enough time to contemplate the best way to shorten them.

Re: C++ says “We have try... finally at home”

#126

Post by actionfromafar »

johnfn wrote: post #73
mort96 wrote: post #9

Earlier quoted context omitted.

Yeah it's a huge mistake IMO. I see it fucking up titles so frequently, and it flies in the face of the "do not editorialise titles" rule: [...] please use the original title, unless it is misleading or linkbait; don't editorialize. It is much worse, I think, to regularly drastically change the meaning of a title automatically until a moderator happens to notice to change it back, than to allow the occasional somewha…

While I disagree with you that it's "a huge mistake" (I think it works fine in 95% of cases), it strikes me that this sort of semantic textual substitution is a perfect task for an LLM. Why not just ask a cheap LLM to de-sensationalize any post which hits more than 50 points or so?

We saw that a few days ago, someone did that.

Re: C++ says “We have try... finally at home”

#127

Post by AnimalMuppet »

locknitpicker wrote: post #121
afiori wrote: post #118

Earlier quoted context omitted.

Ok, but sometimes you just need a single line in a finally and writing a class is more annoying

> Ok, but sometimes you just need a single line in a finally and writing a class is more annoying I don't think you understand. If you need to run cleanup code whenever you need to destroy a resource, there is already a special member function designed to handle that: the destructor. Read up on RAII. It somehow you failed to understand RAII and basic resource management, you can still use one-liners. Read up on scope…

Slightly more than that: If you need to run cleanup code, whatever needs cleaned up should be a class and do the cleanup in the destructor.

Take a file handle, for instance. Don't use open() or fopen() and then try to close it in a finally. Instead, use a file class and let it close itself by going out of scope.

Re: C++ says “We have try... finally at home”

#128

Post by Snarwin »

Someone wrote: post #48
mojuba wrote: post #3

I like how Swift solved this: there's a more universal `defer { ... }` block that's executed at the end of a given scope no matter what, and after the `return` statement is evaluated if it's a function scope. As such it has multiple uses, not just for `try ... finally`.

I think Swift’s defer ( https://docs.swift.org/swift-book/documentation/the-swift-pr... ) was inspired by/copied from go ( https://go.dev/tour/flowcontrol/12 ), but they may have taken it from an even earlier language that I’m not aware of. Defer has two advantages over try…finally: firstly, it doesn’t introduce a nesting level. Secondly, if you write foo defer revert_foo , when scanning the code, it’s easier to veri…

The oldest defer-like feature I can find reference to is the ON_BLOCK_EXIT macro from this article in the December 2000 issue of the C/C++ Users Journal:

https://jacobfilipp.com/DrDobbs/articles/CUJ/2000/cexp1812/a...

A similar macro later (2006) made its way into Boost as BOOST_SCOPE_EXIT:

https://www.boost.org/doc/libs/latest/libs/scope_exit/doc/ht...

I can't say for sure whether Go's creators took inspiration from these, but it wouldn't be surprising if they did.

Re: C++ says “We have try... finally at home”

#129

Post by mort96 »

actionfromafar wrote: post #123
mort96 wrote: post #91

Earlier quoted context omitted.

I agree with this. I don't dislike non-RAII languages (even though I do prefer RAII). I was mostly asking a rhetorical question to point out that it really isn't the same at all. As you say, it's not a RAII language, and you have to think differently than when using a RAII language with proper destructors.

Pondering - is there a language similar to C++ (whatever that means, it's huge, but I guess a sprinkle of don't pay for what you don't use and being compiled) which has no raw pointers and such (sacrificing C compatibility) but which is otherwise pretty similar to C++?

Rust is the only one I really know of. It's many things to many people, but to me as a C++ developer, it's a C++ with a better template model, better object lifetime semantics (destructive moves The biggest essential differences between Rust and C++ are probably the borrow checker (sometimes nice, sometimes just annoying, IMO) and the lack of class inheritance hierarchies. But both are RAII languages which compile to native code with a minimal runtime, both have a heavy emphasis on generic programming through templates, both have a "C-style syntax" with braces which makes Rust feel relatively familiar despite its ML influence.
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