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add Iter[String]::join #1301

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Merged
merged 5 commits into from
Feb 9, 2025
Merged

add Iter[String]::join #1301

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2b753e8
add Iter[String]::join
hackwaly Dec 5, 2024
71fa22c
rename label to sep
hackwaly Jan 20, 2025
a79fcb2
remove cold path
hackwaly Jan 20, 2025
4b46975
change sep to positional argument
hackwaly Jan 21, 2025
4c313ec
fix style of AI completed code
hackwaly Jan 21, 2025
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1 change: 1 addition & 0 deletions builtin/builtin.mbti
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Original file line number Diff line number Diff line change
Expand Up @@ -243,6 +243,7 @@ impl Iter {
head[A](Self[A]) -> A?
intersperse[A](Self[A], A) -> Self[A]
iter[T](Self[T]) -> Self[T]
join(Self[String], String) -> String
just_run[T](Self[T], (T) -> IterResult) -> Unit
last[A](Self[A]) -> A?
map[T, R](Self[T], (T) -> R) -> Self[R]
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16 changes: 16 additions & 0 deletions builtin/iter.mbt
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Expand Up @@ -778,6 +778,22 @@ pub fn Iter::collect[T](self : Iter[T]) -> Array[T] {
result
}

///|
/// Collects the elements of the iterator into a string.
pub fn join(self : Iter[String], sep : String) -> String {
let buf = StringBuilder::new()
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  1. there are some duplications with Logger::write_iter, can you factor out some common parts
  2. if separator == "" this rarely happens, such optimization is not worth it

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@hackwaly hackwaly Jan 20, 2025 •
edited
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Logger::write_iter has unexpected behavior which turn "Test" to "\"Test\"" before write.

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@gmlewis gmlewis Jan 21, 2025 •
edited
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I vote for sep : String... that way you always see the one argument that is passed to join and it is always extremely clear what the code is doing:

arr.iter().join("")
arr.iter().join(", ")
arr.iter().join(" ")
etc.

Additionally, you don't have the jarring noise of sep= cluttering the code unnecessarily.

And it is much easier to write, and muscle memory takes over so that you don't have to think about it, because joins happen frequently in code.

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Now, if the MoonBit compiler could simply perform the .iter() under the covers whenever an iter is needed where it is obvious that the array must be iterated, then that would get us back to the original, beautiful syntax which was one of the reasons early on that I liked MoonBit so much in the first place!!!

arr.join("")
arr.join(", ")
arr.join(" ")
etc.

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I vote for sep : String... that way you always see the one argument that is passed to join and it is always extremely clear what the code is doing:

arr.iter().join("")
arr.iter().join(", ")
arr.iter().join(" ")
etc.

Additionally, you don't have the jarring noise of sep= cluttering the code unnecessarily.

And it is much easier to write, and muscle memory takes over so that you don't have to think about it, because joins happen frequently in code.

lgtm.

let mut first = true
for str in self {
if first {
first = false
} else {
buf.write_string(sep)
}
buf.write_string(str)
}
buf.to_string()
}

///|
/// Iter itself is an iterator.
/// so that it works with array spread operator. e.g, `[..iter]`
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20 changes: 20 additions & 0 deletions builtin/iter_test.mbt
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Expand Up @@ -543,3 +543,23 @@ test "peek function - random cases" {
let iter5 = [0, 0, 0].iter()
inspect!(iter5.peek(), content="Some(0)")
}

test "@builtin.join/empty_iter" {
let empty_iter : Iter[String] = Iter::empty()
inspect!(empty_iter.join(""), content="")
}

test "@builtin.join/single_element" {
let single_elem_iter : Iter[String] = Iter::singleton("Test")
inspect!(single_elem_iter.join(""), content="Test")
}

test "@builtin.join/multiple_elements_with_separator" {
let iter : Iter[String] = ["A", "B", "C"].iter()
inspect!(iter.join(","), content="A,B,C")
}

test "@builtin.join/multiple_elements_without_separator" {
let iter : Iter[String] = ["A", "B", "C"].iter()
inspect!(iter.join(""), content="ABC")
}
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