2 hours ago
Is "defer" a good pattern? Aren't constructors/destructor pairs, like in C++/Rust, or "with" blocks in Python, better, because you cannot forget to call the destructor. I the first code example in the article, it is easy to omit "defer" and the compiler won't notice.
10 hours ago
Article describes try/finally as a hack to get the effect of defer, but it looks to me like it's the other way around? Try/finally is more traditional, in one form or another.
10 hours ago
It's also necessary here because TypeScript has exceptions and you'd expect your `defer`s to execute even when an exception is thrown.
2 hours ago
Author here. I find try/finally verbose and vulnerable to mistakes. For me, it adds "function noise".
4 hours ago
A (lexically-scoped) defer is a more general than a finally block. You can express finally-block semantics using defer.
It's also more exception-safe when you have more than one throwing call in the try block.
9 hours ago
If the idea of computers is that they remember stuff for you and do stuff for you, then both try/finally and defer seem like hacks to work around not having RAII like e.g. Rust or C++ where resources are closed/disposed of/deallocated automatically.
Try X finally dispose of all resources. X, defer clean up X. Or how about just X and cleanup is done automatically, with the author of the resources deciding what is needed to clean X up.
9 hours ago
JS has the using keyword for this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...
8 hours ago
What if you forget to use that and just use let or const? It is better than plain try-finally or defer because you don't have to remember how to dispose of the resources but in terms of remember to dispose of the resource at all, I don't think that is all that different from Python's with or Java's try-with-resources. You can just forget to use using, with, try-with-resources.
There isn't any way to forget to drop a resource if you have RAII.
6 hours ago
Yes, but you also have this problem with `defer`.
3 hours ago
And try/finally.
2 hours ago
Only when doing stack allocations or reference counting, any other heap management strategy and RAII can't help as well.
For example, combining RAII with lock free data structures, which usually ends up in techniques like hazardous pointers instead.
7 hours ago
it's mesmerizing that the fantastic ergonomics of RAII have not propagated to other languages.
It's way easier to use, much clear, less typing, more predictable runtime behavior.
RAII... terrible name, great concept!
3 hours ago
RAII has complications in GC’d, fuzzy ownership langages, it becomes much less ergonomic there because now passing an RAII object as parameter to a function causes that function to clean it up, so you need additional mechanisms to bypass this. Same if you just poke an RAII object inside a collection.
Traditionally langages with simpler runtimes simply used destructors for this, refcounting made it deterministic (modulo the old reference leak), but more advanced garbage collection schemes made that stop working.
2 hours ago
It only works for stack allocations or when using reference counting, which isn't the ultimate performance of GC algorithms.
5 hours ago
I mean, sure, but RAII (in C++, at least) is implemented the same way as this article: with a try...finally block!
RAII doesn't really fit into every language because they don't all have deterministic destructors/finalizers and objects with scoped lifetimes. Sometimes you only have one but not the other and you definitely need both.
25 minutes ago
that's a very broken metaphor - it might be "similar" to try-finally block if you only have one variable/object following RAII. But try-finally block(s) become complete mess when multiple variables are involved, and again requires way more typing/duplication than RIAA. And "similar" in terms of results, NOT similar in terms of performance as try {} block requires additional instructions to set it up, whereas RIAA is runtime free.
And regarding sibling post about finalizers -- another broken concept as you cant use finalizers with limited resources (ex. graphic contexts, db connections, handles, locks, etc) and then these languages that use finalizers become complete mess if you need to manage such resources.
6 hours ago
Finally isn't bullet proof. If you execute a promise in a try block and it happens to end without resolving, the finally block will be never be executed. Fun stuff.
5 hours ago
defer isn't bullet proof either. I think there's a linter about it and os.Exit.
One can just wrap os.Exit in a helper to get the expected behaviour.
5 hours ago
Also, if you pull the power plug, neither finally blocks nor defers would run. I personally consider it a clear and obvious deficiency in the semantics (and the implementations) of those programming languages but everybody refuses to listen to me.
5 hours ago
I think this is correct behavior.
``` async function run() { try { await new Promise(() => { // The executor function finishes, // but it never calls resolve() or reject(). }); } finally { console.log("cleanup"); } } ```
I never expect cleanup to be logged.
6 hours ago
I built a library to do something similar: https://www.npmjs.com/package/yaplib
defer is the thing I miss the most coming from Go
2 hours ago
Cool! I kinda feel like these should be built-in. But this looks useful for closing the DX gap here.
8 hours ago
Would call stack/source map reasonably work with this?
2 hours ago
Reasonably? Yes. Could probably be made to work well.
$ bat 2.ts
───────────────
1 │ function one() {
2 │ let x = 1;
3 │ defer (() => { throw new Error("thrown from one!"); })()
4 │ x = 2;
5 │ }
6 │ one();
─────┴─────────
$ node 2.js
~/healeycodes-typescript-go/2.js:29
throw _errors_1[0];
^
Error: thrown from one!
at _callee_1 (/Users/andrew/Documents/GitHub/healeycodes-typescript-go/2.js:9:46)
at /Users/andrew/Documents/GitHub/healeycodes-typescript-go/2.js:10:33
at one (/Users/andrew/Documents/GitHub/healeycodes-typescript-go/2.js:22:31)
at Object.<anonymous> (/Users/andrew/Documents/GitHub/healeycodes-typescript-go/2.js:34:1)
at Module._compile (node:internal/modules/cjs/loader:1830:14)
at Object..js (node:internal/modules/cjs/loader:1961:10)
at Module.load (node:internal/modules/cjs/loader:1553:32)
at Module._load (node:internal/modules/cjs/loader:1355:12)
at wrapModuleLoad (node:internal/modules/cjs/loader:255:19)
at Module.executeUserEntryPoint [as runMain (node:internal/modules/run_main:154:5)
Node.js v24.15.0