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// This source file is part of the Swift.org open source project
//
// Copyright 2019 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for Swift project authors
/// IdentifierFactory creates unique identifiers for given elements.
/// It provides an API to map between identifiers and elements and can be used
/// for fast lookups.
public final class IdentifierFactory<T: Hashable> {
public typealias Identifier = Array<T>.Index
public let elements: [T]
private var identifiers: [T: Identifier]
/// Initializes a new factory using a collection of elements.
/// - Parameter elements: Contains all elements which will become valid input for calling `identifier(element:)`.
public init<C>(_ elements: C) where C: Collection, C.Element == T {
self.elements = Array(elements)
var identifierLookup = [T: Identifier](minimumCapacity: self.elements.count)
for (index, element) in elements.enumerated() {
identifierLookup[element] = index
}
self.identifiers = identifierLookup
}
public var count: Int {
return elements.count
}
/// Returns the element for a provided identifier.
/// - Parameter id: An identifier created using `identifier(element:)`
public func element(id: Identifier) -> T {
return elements[id]
}
/// Returns a unique identifier for a given element.
/// - Parameter element: The element must have been part of the collection used in the initialization.
public func identifier(element: T) -> Identifier {
guard let identifier = self.identifiers[element] else {
preconditionFailure("Could not get identifier for \(element) because it was not initially added to the IdentifierFactory.")
}
return identifier
}
}
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