zeus
79 lines
2.8 KiB
Swift
79 lines
2.8 KiB
Swift
import Foundation
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/// `DatabaseCollation` is a custom string comparison function used by SQLite.
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///
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/// See also ``Database/CollationName``.
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///
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/// Related SQLite documentation: <https://www.sqlite.org/datatype3.html#collating_sequences>
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///
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/// ## Topics
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///
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/// ### Creating a Custom Collation
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///
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/// - ``init(_:function:)``
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/// - ``name``
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///
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/// ### Built-in Collations
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///
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/// - ``caseInsensitiveCompare``
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/// - ``localizedCaseInsensitiveCompare``
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/// - ``localizedCompare``
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/// - ``localizedStandardCompare``
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/// - ``unicodeCompare``
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public final class DatabaseCollation {
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/// The name of the collation.
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public let name: String
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let function: (CInt, UnsafeRawPointer?, CInt, UnsafeRawPointer?) -> ComparisonResult
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/// Creates a collation.
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///
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/// For example:
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///
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/// ```swift
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/// let collation = DatabaseCollation("localized_standard") { (string1, string2) in
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/// return (string1 as NSString).localizedStandardCompare(string2)
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/// }
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/// db.add(collation: collation)
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/// try db.execute(sql: "CREATE TABLE file (name TEXT COLLATE localized_standard")
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/// ```
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///
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/// - parameters:
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/// - name: The collation name.
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/// - function: A function that compares two strings.
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public init(_ name: String, function: @escaping (String, String) -> ComparisonResult) {
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self.name = name
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self.function = { (length1, buffer1, length2, buffer2) in
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// Buffers are not C strings: they do not end with \0.
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let string1 = String(
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bytesNoCopy: UnsafeMutableRawPointer(mutating: buffer1.unsafelyUnwrapped),
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length: Int(length1),
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encoding: .utf8,
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freeWhenDone: false)!
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let string2 = String(
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bytesNoCopy: UnsafeMutableRawPointer(mutating: buffer2.unsafelyUnwrapped),
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length: Int(length2),
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encoding: .utf8,
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freeWhenDone: false)!
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return function(string1, string2)
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}
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}
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}
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extension DatabaseCollation: Hashable {
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// Collation equality is based on the sqlite3_strnicmp SQLite function.
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// (see https://www.sqlite.org/c3ref/create_collation.html). Computing
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// a hash value that honors the Swift Hashable contract (value equality
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// implies hash equality) is thus non trivial. But it's not that
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// important, since this hashValue is only used when one adds
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// or removes a collation from a database connection.
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public func hash(into hasher: inout Hasher) {
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hasher.combine(0)
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}
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/// Two collations are equal if they share the same name (case insensitive)
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public static func == (lhs: DatabaseCollation, rhs: DatabaseCollation) -> Bool {
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// See <https://www.sqlite.org/c3ref/create_collation.html>
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return sqlite3_stricmp(lhs.name, rhs.name) == 0
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}
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}
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