Fix algorithms overload resolution issues #402
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This change addresses two overload resolution problems with the collection-based algorithm methods. First, when RegexBuilder is imported, `String` gains `RegexComponent` conformance, which means the `RegexComponent`-based overloads win for strings, which is undesirable. Second, if a collection has an element type that can be expressed as an array literal, collection-based methods get selected ahead of any standard library counterpart. These two problems combine in a tricky way for `split` and `contains`. For `split`, both the collection-based and regex-based versions need to be marked as `@_disfavoredOverload` so that the problems above can be resolved. Unfortunately, this sets up an ambiguity once `String` has `RegexComponent` conformance, so the `RegexBuilder` module includes separate overloads for `String` and `Substring` that act as tie-breakers. If introduced in the standard library, these would be a source-breaking change, as they would win over the `Element`- based split when referencing the `split` method, as with `let splitFunction = myString.split`. For `contains`, the same requirements hold, with the added complication that the Foundation overlay defines its own `String.contains(_:)` method with different behavior than included in these additions. For this reason, the more specific overloads for `String` and `Substring` can't live in the `RegexBuilder` module, which creates a problem for source compatibility. As it stands now, this existing code does not compile with the new algorithm methods added, as the type of `vowelPredicate` changes from `(Character) -> Bool` to `(String) -> Bool`: ``` let str = "abcde" let vowelPredicate = "aeiou".contains print(str.filter(vowelPredicate)) ```
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This allows the stdlib's `contains(_:Character)` to be chosen when referenced in an unconstrained context.
This makes sure that a plain String doesn't route through the regex machinery when RegexBuilder is imported.
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Did we discuss or agree to a solution here? |
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No, not yet - this is for discussion in comparison to #411. |
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This change addresses two overload resolution problems with the collection-based algorithm methods. First, when RegexBuilder is imported, `String` gains `RegexComponent` conformance, which means the `RegexComponent`-based overloads win for strings, which is undesirable. Second, if a collection has an element type that can be expressed as an array literal, collection-based methods get selected ahead of any standard library counterpart. These two problems combine in a tricky way for `split` and `contains`. For `split`, both the collection-based and regex-based versions need to be marked as `@_disfavoredOverload` so that the problems above can be resolved. Unfortunately, this sets up an ambiguity once `String` has `RegexComponent` conformance, so the `RegexBuilder` module includes separate overloads for `String` and `Substring` that act as tie-breakers. If introduced in the standard library, these would be a source-breaking change, as they would win over the `Element`- based split when referencing the `split` method, as with `let splitFunction = myString.split`. For `contains`, the same requirements hold, with the added complication that the Foundation overlay defines its own `String.contains(_:)` method with different behavior than included in these additions. For this reason, the more specific overloads for `String` and `Substring` can't live in the `RegexBuilder` module, which creates a problem for source compatibility. As it stands now, this existing code does not compile with the new algorithm methods added, as the type of `vowelPredicate` changes from `(Character) -> Bool` to `(String) -> Bool`: ``` let str = "abcde" let vowelPredicate = "aeiou".contains print(str.filter(vowelPredicate)) ```
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This change addresses two overload resolution problems with the collection-based algorithm methods. First, when RegexBuilder is imported,
StringgainsRegexComponentconformance, which means theRegexComponent-based overloads win for strings, which is undesirable. Second, if a collection has an element type that can be expressed as an array literal, collection-based methods get selected ahead of any standard library counterpart. These two problems combine in a tricky way forsplitandcontains.For
split, both the collection-based and regex-based versions need to be marked as@_disfavoredOverloadso that the problems above can be resolved. Unfortunately, this sets up an ambiguity onceStringhasRegexComponentconformance, so theRegexBuildermodule includes separate overloads forStringandSubstringthat act as tie-breakers. If introduced in the standard library, these would be a source-breaking change, as they would win over theElement-based split when referencing thesplitmethod, as withlet splitFunction = myString.split.For
contains, the same requirements hold, with the added complication that the Foundation overlay defines its ownString.contains(_:)method with different behavior than included in these additions. For this reason, the more specific overloads forStringandSubstringcan't live in theRegexBuildermodule, which creates a problem for source compatibility. As it stands now, this existing code does not compile with the new algorithm methods added, as the type ofvowelPredicatechanges from(Character) -> Boolto(String) -> Bool: