5 ms·

How do immutable variables work with something like a for loop?

foxygen 11mo ago
You use something else like map/filter/reduce or recursion.
tgv 11mo ago
Unless you need the index, you can write: for (const x of iterable) { ... } or for (const attribute in keyValueMap) { ... }. However, loops often change state, so it's probably not the way to go if you can't change any variable.
- Cthulhu_ 11mo ago
  If you need the index, you can use .keys() or .entries() on the iterable, e.g. for (const [index, value] of ["a", "b", "c", "d", "e"].entries()) { console.log(index, value); } Or forEach, or map. Basically, use a higher level language. The traditional for loop tells an interpreter "how" to do things, but unless you need the low level performance, it's better to tell it "what", that is, use more functional programming constructs. This is also the way to go for immutable variables, generally speaking.
  - tgv 11mo ago
    There's no difference between for (x of a) stmt; and a.forEach(x => stmt), except for scope, and lack of flow control in forEach. There's no reason to prefer .forEach(). I don't see how it is "more functional."
tantalor 11mo ago
Is TFA (or anyone else for that matter) actually concerned with "immutable variables"? e.g., `let i = 0; i++;` They seem to be only worried about modifying objects, not reassignment of variables.
- voidUpdate 11mo ago
  Looks like Rust is https://doc.rust-lang.org/stable/std/keyword.let.html https://doc.rust-lang.org/stable/std/keyword.let.html
- macintux 11mo ago
  Erlang doesn't allow variable reassignment. Elixir apparently does, but I've never played with it.
- ruined 11mo ago
  typescript handles that well already
- Cthulhu_ 11mo ago
  That's probably because reassignment is already covered by using `const`. Of course, it doesn't help that the immutable modifier for Swift is `let`. But also, in Swift, if you assign a list via `let`, the list is also immutable.
bastawhiz 11mo ago
Since sibling comments have pointed out the various ES5 methods and ES6 for-of loops, I'll note two things: 1. This isn't an effort to make all variables `const`. It's an effort to make all objects immutable. You can still reassign any variable, just not mutate objects on the heap (by default) 2. Recursion still works ;)
turboponyy 11mo ago
`for` loops are a superfluous language feature if your collections have `map` for transformations and `forEach` for producing side effects
nurettin 11mo ago
They don't work. The language has to provide list and map operations to compensate.

You use something else like map/filter/reduce or recursion.

tgv 11mo ago

Unless you need the index, you can write: for (const x of iterable) { ... } or for (const attribute in keyValueMap) { ... }. However, loops often change state, so it's probably not the way to go if you can't change any variable.

Cthulhu_ 11mo ago
If you need the index, you can use .keys() or .entries() on the iterable, e.g. for (const [index, value] of ["a", "b", "c", "d", "e"].entries()) { console.log(index, value); } Or forEach, or map. Basically, use a higher level language. The traditional for loop tells an interpreter "how" to do things, but unless you need the low level performance, it's better to tell it "what", that is, use more functional programming constructs. This is also the way to go for immutable variables, generally speaking.
- tgv 11mo ago
  There's no difference between for (x of a) stmt; and a.forEach(x => stmt), except for scope, and lack of flow control in forEach. There's no reason to prefer .forEach(). I don't see how it is "more functional."

tantalor 11mo ago

Is TFA (or anyone else for that matter) actually concerned with "immutable variables"? e.g., `let i = 0; i++;` They seem to be only worried about modifying objects, not reassignment of variables.

voidUpdate 11mo ago
Looks like Rust is https://doc.rust-lang.org/stable/std/keyword.let.html https://doc.rust-lang.org/stable/std/keyword.let.html
macintux 11mo ago
Erlang doesn't allow variable reassignment. Elixir apparently does, but I've never played with it.
ruined 11mo ago
typescript handles that well already
Cthulhu_ 11mo ago
That's probably because reassignment is already covered by using `const`. Of course, it doesn't help that the immutable modifier for Swift is `let`. But also, in Swift, if you assign a list via `let`, the list is also immutable.

bastawhiz 11mo ago

Since sibling comments have pointed out the various ES5 methods and ES6 for-of loops, I'll note two things: 1. This isn't an effort to make all variables `const`. It's an effort to make all objects immutable. You can still reassign any variable, just not mutate objects on the heap (by default) 2. Recursion still works ;)

turboponyy 11mo ago

`for` loops are a superfluous language feature if your collections have `map` for transformations and `forEach` for producing side effects

nurettin 11mo ago

They don't work. The language has to provide list and map operations to compensate.