Add String.reverse method

[Chaosus]

Adds a simple method to return the copy of the string in reverse order. May be useful in some cases. Closes godotengine/godot-proposals#3503

[RedworkDE]

1. This implementation breaks some characters, eg "🇺🇦".reverse() == "🇦🇺"
2. Generally you would want to keep unicode grapheme clusters intact and just reverse their order, but in some locales a grapheme cluster is basically an entire word, so there it's probably not what you want either.
3. C# doesn't have this built-in because of exactly such problems, also its naive implementation would give different results.

TL/DR: this is a hard problem and I don't think this implementation does it justice.

[AThousandShips]

I think the quirks of reversing should be documented as per the above mentioned

[dalexeev]

@RedworkDE This is a good point, but note that some graphemes are composed of multiple code points:

print("🇺🇦".length()) # 2

I think we can just document that the reverse() method considers code points under individual characters, not graphemes (sorry if I misused the terms).

[AThousandShips]

Something like:
Note: This treats individual Unicode codepoints as individual characters and does not respect clusters of codepoints, and may cause unexpected behaviour when reversing sequences including emoji, flags, etc.

[Zireael07]

I don't know a reverse() implementation that does NOT break flags/emoji and the like. Should be documented and that's all.

[akien-mga]

This implementation breaks some characters, eg "🇺🇦".reverse() == "🇦🇺"

I believe that's a feature, Australia is upside down :o) @BastiaanOlij

[bruvzg]

This implementation breaks some characters, eg "🇺🇦".reverse() == "🇦🇺"

None of the other String functions will handle composite emojis as a single character, so this is not an issue. Besides this, the result reversing string won't make any sense in many cases (any context dependent character combinations, combining diacritics etc.).

[YuriSizov]

I agree that we shouldn't worry ourselves too much with how it handles complex unicode sequences and various composite languages. The resulting string won't be a valid word or sentence in practically any language. The application for this method lies somewhere else. Though the proposal doesn't elaborate why this is needed, only that it's needed.

If we seriously want to discuss if this is worth it or not, the proposal must provide some details for a use case of reversing a string, and doing so especially efficiently too, to be considered for a built-in (cc @me2beats). But we may also just YOLO this, as the naive implementation is pretty straightforward.

[me2beats]

I used string reverse mainly for searching replacing and sorting
with and without Regex

also can be used in some algorithms for example for procedural generation of names

[akien-mga]

The implementation is straightforward, and it seems like a useful addition for the String class.

It's always hard to know what's the threshold for accepting new helper methods in core, but this seems OK to me, and nobody voiced any specific concerns in the past few weeks.

[akien-mga]

Thanks!