How can I disambiguate a type and a module with the same name?

Question

I'm trying to use Károly Lőrentey's B-tree based OrderedSet in a project. However, I'm running into an issue where I can't declare an unqualified OrderedSet<T> because the name conflicts between Foundation's NSOrderedSet (imported as OrderedSet in Swift 3) and BTree 's OrderedSet .

let set = OrderedSet<Int>()
// error: 'OrderedSet' is ambiguous for type lookup in this context
// Found this candidate: Foundation.OrderedSet:3:14
// Found this candidate: BTree.OrderedSet:12:15

To resolve this conflict, you would normally qualify the name, and that would give you BTree.OrderedSet<T> . However, the BTree module also contains a class named BTree . If I write BTree.OrderedSet , Swift thinks that I'm referring to a type named OrderedSet that is nested in the BTree.BTree type.

let set = BTree.OrderedSet<Int>()
// error: reference to generic type 'BTree' requires arguments in <...>

If I don't import BTree , I can't use the BTree name at all.

// no import BTree
let set = BTree.OrderedSet<Int>()
// error: use of undeclared type 'BTree'

How can I resolve this ambiguity between the BTree type and the BTree module?

Answer 1

The type can be disambiguated using the little-known import (class|struct|func|protocol|enum) Module.Symbol syntax.

import struct BTree.OrderedSet

From this point on, OrderedSet unambiguously refers to the one in BTree.

If this would still be ambiguous or sub-optimal in some files, you can create a Swift file to rename imports using typealiases:

// a.swift
import struct BTree.OrderedSet
typealias BTreeOrderedSet<T> = BTree.OrderedSet<T>

// b.swift
let foo = OrderedSet<Int>() // from Foundation
let bar = BTreeOrderedSet<Int>() // from BTree

There was a new syntax discussed for Swift 3, but it fell through.

Answer 2

我在OrderedSet的Swift 3版本BTree重命名为SortedSet ，这在解决/实现可能的语言级别修复时应作为变通方法。