1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
use crate::fmt;
use crate::hash::Hash;

/// 无限制范围 (`..`)。
///
/// `RangeFull` 主要用作 [切片索引][slicing index],其简写为 `..`。
/// 它不能用作 [`Iterator`],因为它没有起点。
///
/// # Examples
///
/// `..` 语法是一个 `RangeFull`:
///
/// ```
/// assert_eq!((..), std::ops::RangeFull);
/// ```
///
/// 它没有 [`IntoIterator`] 实现,因此不能直接在 `for` 循环中使用它。
/// 这不会编译:
///
/// ```compile_fail,E0277
/// for i in .. {
///     // ...
/// }
/// ```
///
/// 用作 [切片索引][slicing index] 时,`RangeFull` 产生完整的阵列作为切片。
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]); // 这是 `RangeFull`
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
#[lang = "RangeFull"]
#[doc(alias = "..")]
#[derive(Copy, Clone, Default, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeFull;

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for RangeFull {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..")
    }
}

/// (half-open) 范围包括在 (`start..end`) 之下和仅在 (`start..end`) 之上。
///
///
/// 范围 `start..end` 包含 `start <= x < end` 的所有值。
/// 如果为 `start >= end`,则为空。
///
/// # Examples
///
/// `start..end` 语法是 `Range`:
///
/// ```
/// assert_eq!((3..5), std::ops::Range { start: 3, end: 5 });
/// assert_eq!(3 + 4 + 5, (3..6).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]); // 这是 `Range`
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
#[lang = "Range"]
#[doc(alias = "..")]
#[derive(Clone, Default, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Range<Idx> {
    /// 范围的下限 (包括)。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub start: Idx,
    /// 范围 (exclusive) 的上限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub end: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> Range<Idx> {
    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..5).contains(&2));
    /// assert!( (3..5).contains(&3));
    /// assert!( (3..5).contains(&4));
    /// assert!(!(3..5).contains(&5));
    ///
    /// assert!(!(3..3).contains(&3));
    /// assert!(!(3..2).contains(&3));
    ///
    /// assert!( (0.0..1.0).contains(&0.5));
    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }

    /// 如果范围不包含任何项,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..5).is_empty());
    /// assert!( (3..3).is_empty());
    /// assert!( (3..2).is_empty());
    /// ```
    ///
    /// 如果任何一方都无法比拟,则范围为空:
    ///
    /// ```
    /// assert!(!(3.0..5.0).is_empty());
    /// assert!( (3.0..f32::NAN).is_empty());
    /// assert!( (f32::NAN..5.0).is_empty());
    /// ```
    #[stable(feature = "range_is_empty", since = "1.47.0")]
    pub fn is_empty(&self) -> bool {
        !(self.start < self.end)
    }
}

/// 范围仅包括 (`start..`) 以下的范围。
///
/// `RangeFrom` `start..` 包含 `x >= start` 的所有值。
///
/// *Note*: [`Iterator`] 实现中的溢出 (当所包含的数据类型达到其数值限制时) 允许 panic,自动换行或饱和。
/// 此行为由 [`Step`] trait 的实现定义。
/// 对于原始整数,这遵循正常规则,并遵守溢出检查配置文件 (调试中为 panic,释放中为包装)。
/// 还要注意,溢出发生的时间比您想像的要早:溢出发生在 `next` 的调用中,该调用会产生最大值,因为必须将范围设置为产生下一个值的状态。
///
///
/// [`Step`]: crate::iter::Step
///
/// # Examples
///
/// `start..` 语法是 `RangeFrom`:
///
/// ```
/// assert_eq!((2..), std::ops::RangeFrom { start: 2 });
/// assert_eq!(2 + 3 + 4, (2..).take(3).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]); // 这是 `RangeFrom`
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
///
///
#[lang = "RangeFrom"]
#[doc(alias = "..")]
#[derive(Clone, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeFrom<Idx> {
    /// 范围的下限 (包括)。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub start: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..")?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..).contains(&2));
    /// assert!( (3..).contains(&3));
    /// assert!( (3..).contains(&1_000_000_000));
    ///
    /// assert!( (0.0..).contains(&0.5));
    /// assert!(!(0.0..).contains(&f32::NAN));
    /// assert!(!(f32::NAN..).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

/// 范围仅排在 (`..end`) 之上。
///
/// `RangeTo` `..end` 包含 `x < end` 的所有值。
/// 它不能用作 [`Iterator`],因为它没有起点。
///
/// # Examples
///
/// `..end` 语法是 `RangeTo`:
///
/// ```
/// assert_eq!((..5), std::ops::RangeTo { end: 5 });
/// ```
///
/// 它没有 [`IntoIterator`] 实现,因此不能直接在 `for` 循环中使用它。
/// 这不会编译:
///
/// ```compile_fail,E0277
/// // error[E0277]: the trait bound `std::ops::RangeTo<{integer}>:
/// // std::Iterator` 不满足
/// for i in ..5 {
///     // ...
/// }
/// ```
///
/// 当用作 [切片索引][slicing index] 时,`RangeTo` 会在 `end` 所指示的索引之前生成所有数组元素的切片。
///
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]); // 这是 `RangeTo`
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
#[lang = "RangeTo"]
#[doc(alias = "..")]
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeTo<Idx> {
    /// 范围 (exclusive) 的上限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub end: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeTo<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (..5).contains(&-1_000_000_000));
    /// assert!( (..5).contains(&4));
    /// assert!(!(..5).contains(&5));
    ///
    /// assert!( (..1.0).contains(&0.5));
    /// assert!(!(..1.0).contains(&f32::NAN));
    /// assert!(!(..f32::NAN).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

/// 范围包括 (`start..=end`) 的上下边界。
///
/// `RangeInclusive` `start..=end` 包含 `x >= start` 和 `x <= end` 的所有值。除非 `start <= end`,否则为空。
///
/// 这个迭代器是 [fused],但是迭代完成后 `start` 和 `end` 的特定值是未指定的,除了 [`.is_empty()`] 之外,一旦不再产生值,就会返回 `true`。
///
///
/// [fused]: crate::iter::FusedIterator
/// [`.is_empty()`]: RangeInclusive::is_empty
///
/// # Examples
///
/// `start..=end` 语法是 `RangeInclusive`:
///
/// ```
/// assert_eq!((3..=5), std::ops::RangeInclusive::new(3, 5));
/// assert_eq!(3 + 4 + 5, (3..=5).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]); // 这是 `RangeInclusive`
/// ```
///
///
#[lang = "RangeInclusive"]
#[doc(alias = "..=")]
#[derive(Clone, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "inclusive_range", since = "1.26.0")]
pub struct RangeInclusive<Idx> {
    // 请注意,此处的字段不是公开的,以允许更改 future 中的表示形式。尤其是,尽管我们可能公开 start/end,但在不更改 (future/current) 私有字段的情况下对其进行修改可能会导致错误的行为,因此我们不希望支持该模式。
    //
    //
    //
    //
    pub(crate) start: Idx,
    pub(crate) end: Idx,

    // 该字段是:
    //  - 构建时为 `false`
    //  - `false` 当迭代产生一个元素并且迭代器没有耗尽时
    //  - `true` 当迭代已被用于耗尽迭代器时
    //
    // 这是支持 PartialEq 和 Hash 而没有 PartialOrd 绑定或特殊化所必需的。
    pub(crate) exhausted: bool,
}

impl<Idx> RangeInclusive<Idx> {
    /// 创建一个新的包含范围。等同于编写 `start..=end`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ops::RangeInclusive;
    ///
    /// assert_eq!(3..=5, RangeInclusive::new(3, 5));
    /// ```
    #[lang = "range_inclusive_new"]
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[inline]
    #[rustc_promotable]
    #[rustc_const_stable(feature = "const_range_new", since = "1.32.0")]
    pub const fn new(start: Idx, end: Idx) -> Self {
        Self { start, end, exhausted: false }
    }

    /// 返回范围的下限 (包括下限)。
    ///
    /// 当使用包含范围进行迭代时,在迭代结束后未指定 `start()` 和 [`end()`] 的值。
    /// 若要确定包含范围是否为空,请使用 [`is_empty()`] 方法而不是比较 `start() > end()`。
    ///
    /// Note: 范围迭代到穷竭之后,此方法返回的值是不确定的。
    ///
    /// [`end()`]: RangeInclusive::end
    /// [`is_empty()`]: RangeInclusive::is_empty
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).start(), &3);
    /// ```
    ///
    ///
    ///
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    #[inline]
    pub const fn start(&self) -> &Idx {
        &self.start
    }

    /// 返回范围的上限 (包括上限)。
    ///
    /// 当使用包含范围进行迭代时,在迭代结束后未指定 [`start()`] 和 `end()` 的值。
    /// 若要确定包含范围是否为空,请使用 [`is_empty()`] 方法而不是比较 `start() > end()`。
    ///
    /// Note: 范围迭代到穷竭之后,此方法返回的值是不确定的。
    ///
    /// [`start()`]: RangeInclusive::start
    /// [`is_empty()`]: RangeInclusive::is_empty
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).end(), &5);
    /// ```
    ///
    ///
    ///
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    #[inline]
    pub const fn end(&self) -> &Idx {
        &self.end
    }

    /// 将 `RangeInclusive` 分解为 (下限,上限 (含上限))。
    ///
    /// Note: 范围迭代到穷竭之后,此方法返回的值是不确定的。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).into_inner(), (3, 5));
    /// ```
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[inline]
    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
    pub const fn into_inner(self) -> (Idx, Idx) {
        (self.start, self.end)
    }
}

impl RangeInclusive<usize> {
    /// 转换为 `SliceIndex` 实现的专用 `Range`。
    /// 调用者负责处理 `end == usize::MAX`。
    #[inline]
    pub(crate) const fn into_slice_range(self) -> Range<usize> {
        // 如果我们不筋疲力尽,我们只想切片 `start..end + 1`。
        // 如果我们筋疲力尽,则使用 `end + 1..end + 1` 切片会为我们提供一个空范围,该范围仍受该端点的边界检查的影响。
        //
        let exclusive_end = self.end + 1;
        let start = if self.exhausted { exclusive_end } else { self.start };
        start..exclusive_end
    }
}

#[stable(feature = "inclusive_range", since = "1.26.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..=")?;
        self.end.fmt(fmt)?;
        if self.exhausted {
            write!(fmt, " (exhausted)")?;
        }
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..=5).contains(&2));
    /// assert!( (3..=5).contains(&3));
    /// assert!( (3..=5).contains(&4));
    /// assert!( (3..=5).contains(&5));
    /// assert!(!(3..=5).contains(&6));
    ///
    /// assert!( (3..=3).contains(&3));
    /// assert!(!(3..=2).contains(&3));
    ///
    /// assert!( (0.0..=1.0).contains(&1.0));
    /// assert!(!(0.0..=1.0).contains(&f32::NAN));
    /// assert!(!(0.0..=f32::NAN).contains(&0.0));
    /// assert!(!(f32::NAN..=1.0).contains(&1.0));
    /// ```
    ///
    /// 迭代完成后,此方法总是返回 `false`:
    ///
    /// ```
    /// let mut r = 3..=5;
    /// assert!(r.contains(&3) && r.contains(&5));
    /// for _ in r.by_ref() {}
    /// // 此处未指定精确的字段值
    /// assert!(!r.contains(&3) && !r.contains(&5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }

    /// 如果范围不包含任何项,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..=5).is_empty());
    /// assert!(!(3..=3).is_empty());
    /// assert!( (3..=2).is_empty());
    /// ```
    ///
    /// 如果任何一方都无法比拟,则范围为空:
    ///
    /// ```
    /// assert!(!(3.0..=5.0).is_empty());
    /// assert!( (3.0..=f32::NAN).is_empty());
    /// assert!( (f32::NAN..=5.0).is_empty());
    /// ```
    ///
    /// 迭代完成后,此方法返回 `true`:
    ///
    /// ```
    /// let mut r = 3..=5;
    /// for _ in r.by_ref() {}
    /// // 此处未指定精确的字段值
    /// assert!(r.is_empty());
    /// ```
    #[stable(feature = "range_is_empty", since = "1.47.0")]
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.exhausted || !(self.start <= self.end)
    }
}

/// 范围仅包括 (`..=end`) 以上的范围。
///
/// `RangeToInclusive` `..=end` 包含 `x <= end` 的所有值。
/// 它不能用作 [`Iterator`],因为它没有起点。
///
/// # Examples
///
/// `..=end` 语法是 `RangeToInclusive`:
///
/// ```
/// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
/// ```
///
/// 它没有 [`IntoIterator`] 实现,因此不能直接在 `for` 循环中使用它。这不会编译:
///
/// ```compile_fail,E0277
/// // error[E0277]: the trait bound `std::ops::RangeToInclusive<{integer}>:
/// // std::Iterator` 不满足
/// for i in ..=5 {
///     // ...
/// }
/// ```
///
/// 当用作 [切片索引][slicing index] 时,`RangeToInclusive` 会生成所有数组元素的切片,直到并包括 `end` 指示的索引。
///
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]); // 这是 `RangeToInclusive`
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
///
#[lang = "RangeToInclusive"]
#[doc(alias = "..=")]
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "inclusive_range", since = "1.26.0")]
pub struct RangeToInclusive<Idx> {
    /// 范围的上限 (包含上限)
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    pub end: Idx,
}

#[stable(feature = "inclusive_range", since = "1.26.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..=")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (..=5).contains(&-1_000_000_000));
    /// assert!( (..=5).contains(&5));
    /// assert!(!(..=5).contains(&6));
    ///
    /// assert!( (..=1.0).contains(&1.0));
    /// assert!(!(..=1.0).contains(&f32::NAN));
    /// assert!(!(..=f32::NAN).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

// RangeToInclusive<Idx> 不能 impl From<RangeTo<Idx>> 因为下溢可能使用 (..0).into ()
//

/// 一系列键的端点。
///
/// # Examples
///
/// 边界是范围端点:
///
/// ```
/// use std::ops::Bound::*;
/// use std::ops::RangeBounds;
///
/// assert_eq!((..100).start_bound(), Unbounded);
/// assert_eq!((1..12).start_bound(), Included(&1));
/// assert_eq!((1..12).end_bound(), Excluded(&12));
/// ```
///
/// 使用 `Bound`s 的元组作为 [`BTreeMap::range`] 的参数。
/// 请注意,在大多数情况下,最好改用范围语法 (`1..5`)。
///
/// ```
/// use std::collections::BTreeMap;
/// use std::ops::Bound::{Excluded, Included, Unbounded};
///
/// let mut map = BTreeMap::new();
/// map.insert(3, "a");
/// map.insert(5, "b");
/// map.insert(8, "c");
///
/// for (key, value) in map.range((Excluded(3), Included(8))) {
///     println!("{key}: {value}");
/// }
///
/// assert_eq!(Some((&3, &"a")), map.range((Unbounded, Included(5))).next());
/// ```
///
/// [`BTreeMap::range`]: ../../std/collections/btree_map/struct.BTreeMap.html#method.range
#[stable(feature = "collections_bound", since = "1.17.0")]
#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
pub enum Bound<T> {
    /// 包容性范围。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Included(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    /// 排他性约束。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Excluded(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    /// 无限端点。指示此方向没有界限。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Unbounded,
}

impl<T> Bound<T> {
    /// 从 `&Bound<T>` 转换为 `Bound<&T>`。
    #[inline]
    #[stable(feature = "bound_as_ref_shared", since = "1.65.0")]
    pub fn as_ref(&self) -> Bound<&T> {
        match *self {
            Included(ref x) => Included(x),
            Excluded(ref x) => Excluded(x),
            Unbounded => Unbounded,
        }
    }

    /// 从 `&mut Bound<T>` 转换为 `Bound<&mut T>`。
    #[inline]
    #[unstable(feature = "bound_as_ref", issue = "80996")]
    pub fn as_mut(&mut self) -> Bound<&mut T> {
        match *self {
            Included(ref mut x) => Included(x),
            Excluded(ref mut x) => Excluded(x),
            Unbounded => Unbounded,
        }
    }

    /// 映射一个 `Bound` 通过将函数应用于包含的值 (包括 `Included` 和 `Excluded`),返回相同类型的 `Bound`。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(bound_map)]
    /// use std::ops::Bound::*;
    ///
    /// let bound_string = Included("Hello, World!");
    ///
    /// assert_eq!(bound_string.map(|s| s.len()), Included(13));
    /// ```
    ///
    /// ```
    /// #![feature(bound_map)]
    /// use std::ops::Bound;
    /// use Bound::*;
    ///
    /// let unbounded_string: Bound<String> = Unbounded;
    ///
    /// assert_eq!(unbounded_string.map(|s| s.len()), Unbounded);
    /// ```
    #[inline]
    #[unstable(feature = "bound_map", issue = "86026")]
    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Bound<U> {
        match self {
            Unbounded => Unbounded,
            Included(x) => Included(f(x)),
            Excluded(x) => Excluded(f(x)),
        }
    }
}

impl<T: Clone> Bound<&T> {
    /// Map 通过克隆绑定的内容将 `Bound<&T>` 更改为 `Bound<T>`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((1..12).start_bound(), Included(&1));
    /// assert_eq!((1..12).start_bound().cloned(), Included(1));
    /// ```
    #[must_use = "`self` will be dropped if the result is not used"]
    #[stable(feature = "bound_cloned", since = "1.55.0")]
    pub fn cloned(self) -> Bound<T> {
        match self {
            Bound::Unbounded => Bound::Unbounded,
            Bound::Included(x) => Bound::Included(x.clone()),
            Bound::Excluded(x) => Bound::Excluded(x.clone()),
        }
    }
}

/// `RangeBounds` 由 Rust 的内置范围类型实现,由 `..`、`a..`、`..b`、`..=c`、`d..e` 或 `f..=g` 等范围语法生成。
///
#[stable(feature = "collections_range", since = "1.28.0")]
pub trait RangeBounds<T: ?Sized> {
    /// 开始索引绑定。
    ///
    /// 以 `Bound` 形式返回起始值。
    ///
    /// # Examples
    ///
    /// ```
    /// # fn main() {
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((..10).start_bound(), Unbounded);
    /// assert_eq!((3..10).start_bound(), Included(&3));
    /// # }
    /// ```
    #[stable(feature = "collections_range", since = "1.28.0")]
    fn start_bound(&self) -> Bound<&T>;

    /// 结束索引绑定。
    ///
    /// 将结束值返回为 `Bound`。
    ///
    /// # Examples
    ///
    /// ```
    /// # fn main() {
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((3..).end_bound(), Unbounded);
    /// assert_eq!((3..10).end_bound(), Excluded(&10));
    /// # }
    /// ```
    #[stable(feature = "collections_range", since = "1.28.0")]
    fn end_bound(&self) -> Bound<&T>;

    /// 如果范围中包含 `item`,则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (3..5).contains(&4));
    /// assert!(!(3..5).contains(&2));
    ///
    /// assert!( (0.0..1.0).contains(&0.5));
    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    #[stable(feature = "range_contains", since = "1.35.0")]
    fn contains<U>(&self, item: &U) -> bool
    where
        T: PartialOrd<U>,
        U: ?Sized + PartialOrd<T>,
    {
        (match self.start_bound() {
            Included(start) => start <= item,
            Excluded(start) => start < item,
            Unbounded => true,
        }) && (match self.end_bound() {
            Included(end) => item <= end,
            Excluded(end) => item < end,
            Unbounded => true,
        })
    }
}

use self::Bound::{Excluded, Included, Unbounded};

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T: ?Sized> RangeBounds<T> for RangeFull {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeFrom<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeTo<T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for Range<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeInclusive<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        if self.exhausted {
            // 当迭代器用尽时,我们通常有 start == end,但我们希望范围显示为空,不包含任何内容。
            //
            Excluded(&self.end)
        } else {
            Included(&self.end)
        }
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeToInclusive<T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
    fn start_bound(&self) -> Bound<&T> {
        match *self {
            (Included(ref start), _) => Included(start),
            (Excluded(ref start), _) => Excluded(start),
            (Unbounded, _) => Unbounded,
        }
    }

    fn end_bound(&self) -> Bound<&T> {
        match *self {
            (_, Included(ref end)) => Included(end),
            (_, Excluded(ref end)) => Excluded(end),
            (_, Unbounded) => Unbounded,
        }
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
    fn start_bound(&self) -> Bound<&T> {
        self.0
    }

    fn end_bound(&self) -> Bound<&T> {
        self.1
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeFrom<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeTo<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for Range<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeInclusive<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeToInclusive<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(self.end)
    }
}

/// `OneSidedRange` 是为一侧无界的内置范围类型实现的。
/// 例如,`a..`、`..b` 和 `..=c` 实现了 `OneSidedRange`,而 `..`、`d..e` 和 `f..=g` 则没有。
///
/// 实现 `OneSidedRange<T>` 的类型必须从 `RangeBounds::start_bound` 或 `RangeBounds::end_bound` 之一返回 `Bound::Unbounded`。
///
///
#[unstable(feature = "one_sided_range", issue = "69780")]
pub trait OneSidedRange<T: ?Sized>: RangeBounds<T> {}

#[unstable(feature = "one_sided_range", issue = "69780")]
impl<T> OneSidedRange<T> for RangeTo<T> where Self: RangeBounds<T> {}

#[unstable(feature = "one_sided_range", issue = "69780")]
impl<T> OneSidedRange<T> for RangeFrom<T> where Self: RangeBounds<T> {}

#[unstable(feature = "one_sided_range", issue = "69780")]
impl<T> OneSidedRange<T> for RangeToInclusive<T> where Self: RangeBounds<T> {}