Hi Brent,
Perhaps the wording would be better phrased as "boundary from
non-uppercase-character to uppercase-character", i.e. numbers and Emoji
are treated the same as lowercase characters and are included in the
original word.
The following are [unit test cases from the associated
PR](https://github.com/apple/swift/pull/12779/files#diff-26b09c16508c21f9f59dcf6c7a41d4b4R422),
which should indicate the behavior implemented here:
```swift
let toSnakeCaseTests = [
("simpleOneTwo", "simple_one_two"),
("myURL", "my_url"),
("singleCharacterAtEndX", "single_character_at_end_x"),
("thisIsAnXMLProperty", "this_is_an_xml_property"),
("single", "single"), // no underscore
("", ""), // don't die on empty string
("a", "a"), // single character
("aA", "a_a"), // two characters
("version4Thing", "version4_thing"), // numerics
("partCAPS", "part_caps"), // only insert underscore before first all
caps
("partCAPSLowerAGAIN", "part_caps_lower_again"), // switch back and
forth caps.
("manyWordsInThisThing", "many_words_in_this_thing"), // simple
lowercase underscore more
("asdfĆqer", "asdf_ćqer"),
("already_snake_case", "already_snake_case"),
("dataPoint22", "data_point22"),
("dataPoint22Word", "data_point22_word"),
("_oneTwoThree", "_one_two_three"),
("oneTwoThree_", "one_two_three_"),
("__oneTwoThree", "__one_two_three"),
("oneTwoThree__", "one_two_three__"),
("_oneTwoThree_", "_one_two_three_"),
("__oneTwoThree", "__one_two_three"),
("__oneTwoThree__", "__one_two_three__"),
("_test", "_test"),
("_test_", "_test_"),
("__test", "__test"),
("test__", "test__"),
("m͉̟̹y̦̳G͍͚͎̳r̤͉̤͕ͅea̲͕t͇̥̼͖U͇̝̠R͙̻̥͓̣L̥̖͎͓̪̫ͅR̩͖̩eq͈͓u̞e̱s̙t̤̺ͅ",
"m͉̟̹y̦̳_g͍͚͎̳r̤͉̤͕ͅea̲͕t͇̥̼͖_u͇̝̠r͙̻̥͓̣l̥̖͎͓̪̫ͅ_r̩͖̩eq͈͓u̞e̱s̙t̤̺ͅ"),
// because Itai wanted to test this
("🐧🐟", "🐧🐟") // fishy emoji example?
]
```
And for completeness, the [complementary test
cases](https://github.com/apple/swift/pull/12779/files#diff-26b09c16508c21f9f59dcf6c7a41d4b4R540):
```swift
let fromSnakeCaseTests = [
("", ""), // don't die on empty string
("a", "a"), // single character
("ALLCAPS", "ALLCAPS"), // If no underscores, we leave the word as-is
("ALL_CAPS", "allCaps"), // Conversion from screaming snake case
("single", "single"), // do not capitalize anything with no
underscore
("snake_case", "snakeCase"), // capitalize a character
("one_two_three", "oneTwoThree"), // more than one word
("one_2_three", "one2Three"), // numerics
("one2_three", "one2Three"), // numerics, part 2
("snake_Ćase", "snakeĆase"), // do not further modify a capitalized
diacritic
("snake_ćase", "snakeĆase"), // capitalize a diacritic
("alreadyCamelCase", "alreadyCamelCase"), // do not modify already
camel case
("__this_and_that", "__thisAndThat"),
("_this_and_that", "_thisAndThat"),
("this__and__that", "thisAndThat"),
("this_and_that__", "thisAndThat__"),
("this_aNd_that", "thisAndThat"),
("_one_two_three", "_oneTwoThree"),
("one_two_three_", "oneTwoThree_"),
("__one_two_three", "__oneTwoThree"),
("one_two_three__", "oneTwoThree__"),
("_one_two_three_", "_oneTwoThree_"),
("__one_two_three", "__oneTwoThree"),
("__one_two_three__", "__oneTwoThree__"),
("_test", "_test"),
("_test_", "_test_"),
("__test", "__test"),
("test__", "test__"),
("_", "_"),
("__", "__"),
("___", "___"),
("m͉̟̹y̦̳G͍͚͎̳r̤͉̤͕ͅea̲͕t͇̥̼͖U͇̝̠R͙̻̥͓̣L̥̖͎͓̪̫ͅR̩͖̩eq͈͓u̞e̱s̙t̤̺ͅ",
"m͉̟̹y̦̳G͍͚͎̳r̤͉̤͕ͅea̲͕t͇̥̼͖U͇̝̠R͙̻̥͓̣L̥̖͎͓̪̫ͅR̩͖̩eq͈͓u̞e̱s̙t̤̺ͅ"),
// because Itai wanted to test this
("🐧_🐟", "🐧🐟") // fishy emoji example?
]
```
— Itai
On 9 Nov 2017, at 5:57, Brent Royal-Gordon via swift-evolution wrote:
> On Nov 6, 2017, at 12:54 PM, Tony Parker via swift-evolution
<[email protected]> wrote:
Converting from camel case to snake case:
1. Splits words at the boundary of lower-case to upper-case
2. Inserts `_` between words
3. Lowercases the entire string
4. Preserves starting and ending `_`.
For example, `oneTwoThree` becomes `one_two_three`. `_oneTwoThree_`
becomes `_one_two_three_`.
My first thought was "are you handling `valueAsHTML` correctly?", but
it looks like you are with the "boundary of lower-case to upper-case"
wording. But what do you plan to do for numbers? Characters in
caseless scripts? Emoji (which are valid in Swift identifiers)? I
don't necessarily have strong opinions about the right answer—just
want to make sure you do *something* about it.
--
Brent Royal-Gordon
Architechies
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