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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”

#31

Post by dist-epoch »

mort96 wrote: post #25
jchw wrote: post #22

Earlier quoted context omitted.

Destructors and finally clauses serve different purposes IMO. Most of the languages that have finally clauses also have destructors. > Syntax is also less cluttered with less indentation, especially when multiple objects are created that require nested try... finally blocks. I think that's more of a point against try...catch/maybe exceptions as a whole, rather than the finally block. (Though I do agree with that. I d…

> Most of the languages that have finally clauses also have destructors. Hm, is that true? I know of finally from Java, JavaScript, C# and Python, and none of them have proper destructors. I mean some of them have object finalizers which can be used to clean up resources whenever the garbage collector comes around to collect the object, but those are not remotely similar to destructors which typically run determinist…

Technically CPython has deterministic destructors, __del__ always gets called immediately when ref count goes to zero, but it's just an implementation detail, not a language spec thing.

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

#32

Post by varjag »

usrnm wrote: post #11
sigmoid10 wrote: post #7

Earlier quoted context omitted.

It does... until you switch employers. Or sometimes even just read a coworker's code. Or even your own older code. Actually no, I don't think anyone achieved full readability enlightenment. People like me just hallucinated it after doing the same things for too long.

And yet, somehow Lisp continues to be everyone's sweetheart, even though creating literal new DSLs for every project is one of the features of the language.

It's because DSLs there reduce cognitive load for the reader rather than add up to it.

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

#33

Post by mojuba »

dwattttt wrote: post #6
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 was contemplating what it would look like to provide this with a macro in Rust, and of course someone has already done it. It's syntactic sugar for the destructor/RAII approach. https://docs.rs/defer-rs/latest/defer_rs/

I don't know Rust but, can this `defer` evaluate after the `return` statement is evaluated like in Swift? Because in Swift you can do this:

    func atomic_get_and_inc() -> Int {
        sem.wait()
        defer {
            value += 1
            sem.signal()
        }
        return value
    }

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

#35

Post by lmz »

vkazanov wrote: post #20
usrnm wrote: post #11

Earlier quoted context omitted.

And yet, somehow Lisp continues to be everyone's sweetheart, even though creating literal new DSLs for every project is one of the features of the language.

Lisp doesnt have much syntax to speak of. All of the DSLs use the same basic structure and are easy to read. Cpp has A LOT A of syntax: init rules, consts, references, move, copy, templates, special cases, etc. It also includes most of C, which is small but has so many basic language design mistakes that "C puzzles" is a book.

The syntax and the concepts (const, move, copy, etc) are orthogonal. You could possibly write a lisp / s-exp syntax for c++ and all it would make better would be the macros in the preprocessor. The DSL doesn't have to be hard to read if it uses unfamiliar/uncommon project specific concepts.

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

#36

Post by usrnm »

varjag wrote: post #32
usrnm wrote: post #11

Earlier quoted context omitted.

And yet, somehow Lisp continues to be everyone's sweetheart, even though creating literal new DSLs for every project is one of the features of the language.

It's because DSLs there reduce cognitive load for the reader rather than add up to it.

Well-designed abstractions do that in every language. And badly designed ones do the opposite, again in all languages. There's nothing special about Lisp here

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

#37

Post by yoshuaw »

winternewt wrote: post #21

Destructors are vastly superior to the finally keyword because they only require us to remember a single time to release resources (in the destructor) as opposed to every finally clause. For example, a file always closes itself when it goes out of scope instead of having to be explicitly closed by the person who opened the file. Syntax is also less cluttered with less indentation, especially when multiple objects are…

I couldn't agree more. And in the rare cases where destructors do need to be created inline, it's not hard to combine destructors with closures into library types.

To point at one example: we recently added `std::mem::DropGuard` [1] to Rust nightly. This makes it easy to quickly create (and dismiss) destructors inline, without the need for any extra keywords or language support.

[1]: https://doc.rust-lang.org/nightly/std/mem/struct.DropGuard.h...

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

#38

Post by jchw »

mort96 wrote: post #25
jchw wrote: post #22

Earlier quoted context omitted.

Destructors and finally clauses serve different purposes IMO. Most of the languages that have finally clauses also have destructors. > Syntax is also less cluttered with less indentation, especially when multiple objects are created that require nested try... finally blocks. I think that's more of a point against try...catch/maybe exceptions as a whole, rather than the finally block. (Though I do agree with that. I d…

> Most of the languages that have finally clauses also have destructors. Hm, is that true? I know of finally from Java, JavaScript, C# and Python, and none of them have proper destructors. I mean some of them have object finalizers which can be used to clean up resources whenever the garbage collector comes around to collect the object, but those are not remotely similar to destructors which typically run determinist…

I don't view finalizers and destructors as different concepts. The notion only matters if you actually need cleanup behavior to be deterministic rather than just eventual, or you are dealing with something like thread locals. (Historically, C# even simply called them destructors.)

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

#39

Post by locknitpicker »

jasode wrote: post #2

The submitted title is missing the salient keyword "finally" that motivates the blog post. The actual subtitle Raymond Chen wrote is: "C++ says “We have try…finally at home.”" It's a snowclone based on the meme, "Mom, can we get ? No, we have at home." : https://www.google.com/search?q=%22we+have+x+at+home%22+meme In other words, Raymond is saying... "We already have Java feature of 'finally' at home in the C++ refri…

> 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. Complaining that you might need to write a class is specious reasoning because if you have a resource worth managing, you already use RAII to manage it. And RAII is one of the most fundamental and defining features of C++.

It all boils down to whether one knows what they are doing, or even bothers to know what they are doing.

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