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In a naive implementation of a Sequence adapter, adapting a non-self-destructive (multi-pass) Sequence having a reference-semantics Generator produces a self-destructive adapted view. This is technically correct because Sequences are allowed to be self-destructive, and theoretically every multi-pass Sequence would be a Collection. However Sequences are much easier to build than Collections, so users are likely to make them, and it would be extremely surprising if adapting a self-preserving Sequence yielded a self-destructive one. Swift SVN r18350
81 lines
2.1 KiB
Swift
81 lines
2.1 KiB
Swift
//===--- Map.swift - tests for lazy mapping -------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See http://swift.org/LICENSE.txt for license information
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// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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// RUN: %target-run-simple-swift | FileCheck %s
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// CHECK: testing...
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println("testing...")
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// Test mapping a collection
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// CHECK-NEXT: [6, 9, 12, 15, 18, 21]
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let a = Array(map(2..8) { $0 * 3 })
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println(a)
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// Test mapping a sequence
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let s = map(a.generate()) { $0 / 3 }
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// CHECK-NEXT: <2, 3, 4, 5, 6, 7>
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print("<")
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var prefix = ""
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for x in s {
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print("\(prefix)\(x)")
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prefix = ", "
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}
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println(">")
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//===--- Avoid creating gratutitously self-destructive sequences ----------===//
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// In a naive implementation, mapping over a non-self-destructive
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// Sequence having a reference-semantics Generator produces a
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// self-destructive mapped view. This is technically correct because
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// Sequences are allowed to be self-destructive, and theoretically
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// every multi-pass Sequence would be a Collection, but Sequences are
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// much easier to build than Collections and it would be extremely
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// surprising for users if their mappings were not stable.
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// A Generator with reference semantics
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class Counter : Generator {
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func next() -> Int? {
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return n < end ? n++ : nil
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}
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init(_ n: Int, _ end: Int) {
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self.n = n
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self.end = end
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}
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var n: Int
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var end: Int
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}
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// A Sequence with value semantics
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struct IntRange: Sequence {
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func generate() -> Counter {
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return Counter(start, end)
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}
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var start: Int
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var end: Int
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}
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// Make sure we can iterate a mapped view of IntRange without
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// consuming it.
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let m1 = map(IntRange(start: 1, end: 5)) { $0 * 2 }
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// CHECK-NEXT: [2, 4, 6, 8]
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println(Array(m1))
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// A second iteration produces the same result.
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// CHECK-NEXT: [2, 4, 6, 8]
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println(Array(m1))
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// CHECK-NEXT: all done.
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println("all done.")
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