[swift-evolution] JSONEncoder: Key strategies

[Itai Ferber]

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 
> <swift-evolution at swift.org> 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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> swift-evolution mailing list
> swift-evolution at swift.org
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