String trimming

[RoBo-Inc]

Currently, the library lacks some string trimming functionality. After some experimentation (and even a draft PR 😳), I came up with these code snippets, which I found quite handy (actually it's like .string, but with trimming along the way):

extension Conversion where Self == AnyConversion<Substring.UTF8View, String> {
    @inlinable
    public static func trimming(
        _ characterSet: CharacterSet = .whitespaces,
        _ including: Character...,
        unapply: @escaping (String) -> any StringProtocol = { " " + $0 }
    ) -> Self {
        .init(apply: {
            let characterSet = characterSet.union(.init(charactersIn: .init(including)))
            return .init(.init(decoding: $0, as: UTF8.self).trimmingCharacters(in: characterSet))
        }, unapply: { Substring(unapply($0)).utf8 })
    }
}

extension Conversion where Self == AnyConversion<Substring, String> {
    @inlinable
    public static func trimming(
        _ characterSet: CharacterSet = .whitespaces,
        _ including: Character...,
        unapply: @escaping (String) -> any StringProtocol = { " " + $0 }
    ) -> AnyConversion<Substring, String> {
        .init(apply: {
            let characterSet = characterSet.union(.init(charactersIn: .init(including)))
            return .init($0.trimmingCharacters(in: characterSet))
        }, unapply: { .init(unapply($0)) })
    }
}

extension Conversion where Output == String {
    @inlinable
    public func trimming(
        _ characterSet: CharacterSet = .whitespaces,
        _ including: Character...,
        unapply: @escaping (String) -> String = { " " + $0 }
    ) -> Conversions.Map<Self, AnyConversion<String, String>> {
        map(.init(apply: {
            let characterSet = characterSet.union(.init(charactersIn: .init(including)))
            return .init($0.trimmingCharacters(in: characterSet))
        }, unapply: unapply))
    }
}

I hope this will be useful to someone. Or maybe the maintainers will even include something like this into the library's codebase 😊

Usage example (inspired by the "Race" sample problem):

PrefixUpTo("°").map(.trimming().toDouble(by: "%.5f"))

.toDouble is a similar set of helper functions that allows printing a Double value in a specific format (like in the "Race" problem, where it's formatted to 5 decimal places: '40.75740')