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
// This file is part of Substrate.

// Copyright (C) 2017-2023 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Traits, types and structs to support a bounded BTreeMap.

use crate::{Get, TryCollect};
use alloc::collections::BTreeMap;
use codec::{Compact, Decode, Encode, MaxEncodedLen};
use core::{borrow::Borrow, marker::PhantomData, ops::Deref};

/// A bounded map based on a B-Tree.
///
/// B-Trees represent a fundamental compromise between cache-efficiency and actually minimizing
/// the amount of work performed in a search. See [`BTreeMap`] for more details.
///
/// Unlike a standard `BTreeMap`, there is an enforced upper limit to the number of items in the
/// map. All internal operations ensure this bound is respected.
#[derive(Encode, scale_info::TypeInfo)]
#[scale_info(skip_type_params(S))]
pub struct BoundedBTreeMap<K, V, S>(BTreeMap<K, V>, PhantomData<S>);

impl<K, V, S> Decode for BoundedBTreeMap<K, V, S>
where
	K: Decode + Ord,
	V: Decode,
	S: Get<u32>,
{
	fn decode<I: codec::Input>(input: &mut I) -> Result<Self, codec::Error> {
		// Same as the underlying implementation for `Decode` on `BTreeMap`, except we fail early if
		// the len is too big.
		let len: u32 = <Compact<u32>>::decode(input)?.into();
		if len > S::get() {
			return Err("BoundedBTreeMap exceeds its limit".into())
		}
		input.descend_ref()?;
		let inner = Result::from_iter((0..len).map(|_| Decode::decode(input)))?;
		input.ascend_ref();
		Ok(Self(inner, PhantomData))
	}

	fn skip<I: codec::Input>(input: &mut I) -> Result<(), codec::Error> {
		BTreeMap::<K, V>::skip(input)
	}
}

impl<K, V, S> BoundedBTreeMap<K, V, S>
where
	S: Get<u32>,
{
	/// Get the bound of the type in `usize`.
	pub fn bound() -> usize {
		S::get() as usize
	}
}

impl<K, V, S> BoundedBTreeMap<K, V, S>
where
	K: Ord,
	S: Get<u32>,
{
	/// Create `Self` from `t` without any checks.
	fn unchecked_from(t: BTreeMap<K, V>) -> Self {
		Self(t, Default::default())
	}

	/// Exactly the same semantics as `BTreeMap::retain`.
	///
	/// The is a safe `&mut self` borrow because `retain` can only ever decrease the length of the
	/// inner map.
	pub fn retain<F: FnMut(&K, &mut V) -> bool>(&mut self, f: F) {
		self.0.retain(f)
	}

	/// Create a new `BoundedBTreeMap`.
	///
	/// Does not allocate.
	pub fn new() -> Self {
		BoundedBTreeMap(BTreeMap::new(), PhantomData)
	}

	/// Consume self, and return the inner `BTreeMap`.
	///
	/// This is useful when a mutating API of the inner type is desired, and closure-based mutation
	/// such as provided by [`try_mutate`][Self::try_mutate] is inconvenient.
	pub fn into_inner(self) -> BTreeMap<K, V> {
		debug_assert!(self.0.len() <= Self::bound());
		self.0
	}

	/// Consumes self and mutates self via the given `mutate` function.
	///
	/// If the outcome of mutation is within bounds, `Some(Self)` is returned. Else, `None` is
	/// returned.
	///
	/// This is essentially a *consuming* shorthand [`Self::into_inner`] -> `...` ->
	/// [`Self::try_from`].
	pub fn try_mutate(mut self, mut mutate: impl FnMut(&mut BTreeMap<K, V>)) -> Option<Self> {
		mutate(&mut self.0);
		(self.0.len() <= Self::bound()).then(move || self)
	}

	/// Clears the map, removing all elements.
	pub fn clear(&mut self) {
		self.0.clear()
	}

	/// Return a mutable reference to the value corresponding to the key.
	///
	/// The key may be any borrowed form of the map's key type, but the ordering on the borrowed
	/// form _must_ match the ordering on the key type.
	pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut V>
	where
		K: Borrow<Q>,
		Q: Ord + ?Sized,
	{
		self.0.get_mut(key)
	}

	/// Exactly the same semantics as [`BTreeMap::insert`], but returns an `Err` (and is a noop) if
	/// the new length of the map exceeds `S`.
	///
	/// In the `Err` case, returns the inserted pair so it can be further used without cloning.
	pub fn try_insert(&mut self, key: K, value: V) -> Result<Option<V>, (K, V)> {
		if self.len() < Self::bound() || self.0.contains_key(&key) {
			Ok(self.0.insert(key, value))
		} else {
			Err((key, value))
		}
	}

	/// Remove a key from the map, returning the value at the key if the key was previously in the
	/// map.
	///
	/// The key may be any borrowed form of the map's key type, but the ordering on the borrowed
	/// form _must_ match the ordering on the key type.
	pub fn remove<Q>(&mut self, key: &Q) -> Option<V>
	where
		K: Borrow<Q>,
		Q: Ord + ?Sized,
	{
		self.0.remove(key)
	}

	/// Remove a key from the map, returning the value at the key if the key was previously in the
	/// map.
	///
	/// The key may be any borrowed form of the map's key type, but the ordering on the borrowed
	/// form _must_ match the ordering on the key type.
	pub fn remove_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>
	where
		K: Borrow<Q>,
		Q: Ord + ?Sized,
	{
		self.0.remove_entry(key)
	}

	/// Gets a mutable iterator over the entries of the map, sorted by key.
	///
	/// See [`BTreeMap::iter_mut`] for more information.
	pub fn iter_mut(&mut self) -> alloc::collections::btree_map::IterMut<K, V> {
		self.0.iter_mut()
	}

	/// Consume the map, applying `f` to each of it's values and returning a new map.
	pub fn map<T, F>(self, mut f: F) -> BoundedBTreeMap<K, T, S>
	where
		F: FnMut((&K, V)) -> T,
	{
		BoundedBTreeMap::<K, T, S>::unchecked_from(
			self.0
				.into_iter()
				.map(|(k, v)| {
					let t = f((&k, v));
					(k, t)
				})
				.collect(),
		)
	}

	/// Consume the map, applying `f` to each of it's values as long as it returns successfully. If
	/// an `Err(E)` is ever encountered, the mapping is short circuited and the error is returned;
	/// otherwise, a new map is returned in the contained `Ok` value.
	pub fn try_map<T, E, F>(self, mut f: F) -> Result<BoundedBTreeMap<K, T, S>, E>
	where
		F: FnMut((&K, V)) -> Result<T, E>,
	{
		Ok(BoundedBTreeMap::<K, T, S>::unchecked_from(
			self.0
				.into_iter()
				.map(|(k, v)| (f((&k, v)).map(|t| (k, t))))
				.collect::<Result<BTreeMap<_, _>, _>>()?,
		))
	}
}

impl<K, V, S> Default for BoundedBTreeMap<K, V, S>
where
	K: Ord,
	S: Get<u32>,
{
	fn default() -> Self {
		Self::new()
	}
}

impl<K, V, S> Clone for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: Clone,
{
	fn clone(&self) -> Self {
		BoundedBTreeMap(self.0.clone(), PhantomData)
	}
}

impl<K, V, S> core::fmt::Debug for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: core::fmt::Debug,
	S: Get<u32>,
{
	fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
		f.debug_tuple("BoundedBTreeMap").field(&self.0).field(&Self::bound()).finish()
	}
}

// Custom implementation of `Hash` since deriving it would require all generic bounds to also
// implement it.
#[cfg(feature = "std")]
impl<K: std::hash::Hash, V: std::hash::Hash, S> std::hash::Hash for BoundedBTreeMap<K, V, S> {
	fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
		self.0.hash(state);
	}
}

impl<K, V, S1, S2> PartialEq<BoundedBTreeMap<K, V, S1>> for BoundedBTreeMap<K, V, S2>
where
	BTreeMap<K, V>: PartialEq,
	S1: Get<u32>,
	S2: Get<u32>,
{
	fn eq(&self, other: &BoundedBTreeMap<K, V, S1>) -> bool {
		S1::get() == S2::get() && self.0 == other.0
	}
}

impl<K, V, S> Eq for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: Eq,
	S: Get<u32>,
{
}

impl<K, V, S> PartialEq<BTreeMap<K, V>> for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: PartialEq,
{
	fn eq(&self, other: &BTreeMap<K, V>) -> bool {
		self.0 == *other
	}
}

impl<K, V, S> PartialOrd for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: PartialOrd,
	S: Get<u32>,
{
	fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
		self.0.partial_cmp(&other.0)
	}
}

impl<K, V, S> Ord for BoundedBTreeMap<K, V, S>
where
	BTreeMap<K, V>: Ord,
	S: Get<u32>,
{
	fn cmp(&self, other: &Self) -> core::cmp::Ordering {
		self.0.cmp(&other.0)
	}
}

impl<K, V, S> IntoIterator for BoundedBTreeMap<K, V, S> {
	type Item = (K, V);
	type IntoIter = alloc::collections::btree_map::IntoIter<K, V>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.into_iter()
	}
}

impl<'a, K, V, S> IntoIterator for &'a BoundedBTreeMap<K, V, S> {
	type Item = (&'a K, &'a V);
	type IntoIter = alloc::collections::btree_map::Iter<'a, K, V>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.iter()
	}
}

impl<'a, K, V, S> IntoIterator for &'a mut BoundedBTreeMap<K, V, S> {
	type Item = (&'a K, &'a mut V);
	type IntoIter = alloc::collections::btree_map::IterMut<'a, K, V>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.iter_mut()
	}
}

impl<K, V, S> MaxEncodedLen for BoundedBTreeMap<K, V, S>
where
	K: MaxEncodedLen,
	V: MaxEncodedLen,
	S: Get<u32>,
{
	fn max_encoded_len() -> usize {
		Self::bound()
			.saturating_mul(K::max_encoded_len().saturating_add(V::max_encoded_len()))
			.saturating_add(codec::Compact(S::get()).encoded_size())
	}
}

impl<K, V, S> Deref for BoundedBTreeMap<K, V, S>
where
	K: Ord,
{
	type Target = BTreeMap<K, V>;

	fn deref(&self) -> &Self::Target {
		&self.0
	}
}

impl<K, V, S> AsRef<BTreeMap<K, V>> for BoundedBTreeMap<K, V, S>
where
	K: Ord,
{
	fn as_ref(&self) -> &BTreeMap<K, V> {
		&self.0
	}
}

impl<K, V, S> From<BoundedBTreeMap<K, V, S>> for BTreeMap<K, V>
where
	K: Ord,
{
	fn from(map: BoundedBTreeMap<K, V, S>) -> Self {
		map.0
	}
}

impl<K, V, S> TryFrom<BTreeMap<K, V>> for BoundedBTreeMap<K, V, S>
where
	K: Ord,
	S: Get<u32>,
{
	type Error = ();

	fn try_from(value: BTreeMap<K, V>) -> Result<Self, Self::Error> {
		(value.len() <= Self::bound())
			.then(move || BoundedBTreeMap(value, PhantomData))
			.ok_or(())
	}
}

impl<K, V, S> codec::DecodeLength for BoundedBTreeMap<K, V, S> {
	fn len(self_encoded: &[u8]) -> Result<usize, codec::Error> {
		// `BoundedBTreeMap<K, V, S>` is stored just a `BTreeMap<K, V>`, which is stored as a
		// `Compact<u32>` with its length followed by an iteration of its items. We can just use
		// the underlying implementation.
		<BTreeMap<K, V> as codec::DecodeLength>::len(self_encoded)
	}
}

impl<K, V, S> codec::EncodeLike<BTreeMap<K, V>> for BoundedBTreeMap<K, V, S> where BTreeMap<K, V>: Encode {}

impl<I, K, V, Bound> TryCollect<BoundedBTreeMap<K, V, Bound>> for I
where
	K: Ord,
	I: ExactSizeIterator + Iterator<Item = (K, V)>,
	Bound: Get<u32>,
{
	type Error = &'static str;

	fn try_collect(self) -> Result<BoundedBTreeMap<K, V, Bound>, Self::Error> {
		if self.len() > Bound::get() as usize {
			Err("iterator length too big")
		} else {
			Ok(BoundedBTreeMap::<K, V, Bound>::unchecked_from(self.collect::<BTreeMap<K, V>>()))
		}
	}
}

#[cfg(test)]
mod test {
	use super::*;
	use crate::ConstU32;
	use alloc::{vec, vec::Vec};
	use codec::CompactLen;

	fn map_from_keys<K>(keys: &[K]) -> BTreeMap<K, ()>
	where
		K: Ord + Copy,
	{
		keys.iter().copied().zip(core::iter::repeat(())).collect()
	}

	fn boundedmap_from_keys<K, S>(keys: &[K]) -> BoundedBTreeMap<K, (), S>
	where
		K: Ord + Copy,
		S: Get<u32>,
	{
		map_from_keys(keys).try_into().unwrap()
	}

	#[test]
	fn encoding_same_as_unbounded_map() {
		let b = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2, 3, 4, 5, 6]);
		let m = map_from_keys(&[1, 2, 3, 4, 5, 6]);

		assert_eq!(b.encode(), m.encode());
	}

	#[test]
	fn try_insert_works() {
		let mut bounded = boundedmap_from_keys::<u32, ConstU32<4>>(&[1, 2, 3]);
		bounded.try_insert(0, ()).unwrap();
		assert_eq!(*bounded, map_from_keys(&[1, 0, 2, 3]));

		assert!(bounded.try_insert(9, ()).is_err());
		assert_eq!(*bounded, map_from_keys(&[1, 0, 2, 3]));
	}

	#[test]
	fn deref_coercion_works() {
		let bounded = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2, 3]);
		// these methods come from deref-ed vec.
		assert_eq!(bounded.len(), 3);
		assert!(bounded.iter().next().is_some());
		assert!(!bounded.is_empty());
	}

	#[test]
	fn try_mutate_works() {
		let bounded = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2, 3, 4, 5, 6]);
		let bounded = bounded
			.try_mutate(|v| {
				v.insert(7, ());
			})
			.unwrap();
		assert_eq!(bounded.len(), 7);
		assert!(bounded
			.try_mutate(|v| {
				v.insert(8, ());
			})
			.is_none());
	}

	#[test]
	fn btree_map_eq_works() {
		let bounded = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2, 3, 4, 5, 6]);
		assert_eq!(bounded, map_from_keys(&[1, 2, 3, 4, 5, 6]));
	}

	#[test]
	fn too_big_fail_to_decode() {
		let v: Vec<(u32, u32)> = vec![(1, 1), (2, 2), (3, 3), (4, 4), (5, 5)];
		assert_eq!(
			BoundedBTreeMap::<u32, u32, ConstU32<4>>::decode(&mut &v.encode()[..]),
			Err("BoundedBTreeMap exceeds its limit".into()),
		);
	}

	#[test]
	fn dont_consume_more_data_than_bounded_len() {
		let m = map_from_keys(&[1, 2, 3, 4, 5, 6]);
		let data = m.encode();
		let data_input = &mut &data[..];

		BoundedBTreeMap::<u32, u32, ConstU32<4>>::decode(data_input).unwrap_err();
		assert_eq!(data_input.len(), data.len() - Compact::<u32>::compact_len(&(data.len() as u32)));
	}

	#[test]
	fn unequal_eq_impl_insert_works() {
		// given a struct with a strange notion of equality
		#[derive(Debug)]
		struct Unequal(u32, bool);

		impl PartialEq for Unequal {
			fn eq(&self, other: &Self) -> bool {
				self.0 == other.0
			}
		}
		impl Eq for Unequal {}

		impl Ord for Unequal {
			fn cmp(&self, other: &Self) -> core::cmp::Ordering {
				self.0.cmp(&other.0)
			}
		}

		impl PartialOrd for Unequal {
			fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
				Some(self.cmp(other))
			}
		}

		let mut map = BoundedBTreeMap::<Unequal, u32, ConstU32<4>>::new();

		// when the set is full

		for i in 0..4 {
			map.try_insert(Unequal(i, false), i).unwrap();
		}

		// can't insert a new distinct member
		map.try_insert(Unequal(5, false), 5).unwrap_err();

		// but _can_ insert a distinct member which compares equal, though per the documentation,
		// neither the set length nor the actual member are changed, but the value is
		map.try_insert(Unequal(0, true), 6).unwrap();
		assert_eq!(map.len(), 4);
		let (zero_key, zero_value) = map.get_key_value(&Unequal(0, true)).unwrap();
		assert_eq!(zero_key.0, 0);
		assert_eq!(zero_key.1, false);
		assert_eq!(*zero_value, 6);
	}

	#[test]
	fn eq_works() {
		// of same type
		let b1 = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2]);
		let b2 = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2]);
		assert_eq!(b1, b2);

		// of different type, but same value and bound.
		crate::parameter_types! {
			B1: u32 = 7;
			B2: u32 = 7;
		}
		let b1 = boundedmap_from_keys::<u32, B1>(&[1, 2]);
		let b2 = boundedmap_from_keys::<u32, B2>(&[1, 2]);
		assert_eq!(b1, b2);
	}

	#[test]
	fn can_be_collected() {
		let b1 = boundedmap_from_keys::<u32, ConstU32<5>>(&[1, 2, 3, 4]);
		let b2: BoundedBTreeMap<u32, (), ConstU32<5>> = b1.iter().map(|(k, v)| (k + 1, *v)).try_collect().unwrap();
		assert_eq!(b2.into_iter().map(|(k, _)| k).collect::<Vec<_>>(), vec![2, 3, 4, 5]);

		// can also be collected into a collection of length 4.
		let b2: BoundedBTreeMap<u32, (), ConstU32<4>> = b1.iter().map(|(k, v)| (k + 1, *v)).try_collect().unwrap();
		assert_eq!(b2.into_iter().map(|(k, _)| k).collect::<Vec<_>>(), vec![2, 3, 4, 5]);

		// can be mutated further into iterators that are `ExactSizedIterator`.
		let b2: BoundedBTreeMap<u32, (), ConstU32<5>> =
			b1.iter().map(|(k, v)| (k + 1, *v)).rev().skip(2).try_collect().unwrap();
		// note that the binary tree will re-sort this, so rev() is not really seen
		assert_eq!(b2.into_iter().map(|(k, _)| k).collect::<Vec<_>>(), vec![2, 3]);

		let b2: BoundedBTreeMap<u32, (), ConstU32<5>> =
			b1.iter().map(|(k, v)| (k + 1, *v)).take(2).try_collect().unwrap();
		assert_eq!(b2.into_iter().map(|(k, _)| k).collect::<Vec<_>>(), vec![2, 3]);

		// but these won't work
		let b2: Result<BoundedBTreeMap<u32, (), ConstU32<3>>, _> = b1.iter().map(|(k, v)| (k + 1, *v)).try_collect();
		assert!(b2.is_err());

		let b2: Result<BoundedBTreeMap<u32, (), ConstU32<1>>, _> =
			b1.iter().map(|(k, v)| (k + 1, *v)).skip(2).try_collect();
		assert!(b2.is_err());
	}

	#[test]
	fn test_iter_mut() {
		let mut b1: BoundedBTreeMap<u8, u8, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k)).try_collect().unwrap();

		let b2: BoundedBTreeMap<u8, u8, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k * 2)).try_collect().unwrap();

		b1.iter_mut().for_each(|(_, v)| *v *= 2);

		assert_eq!(b1, b2);
	}

	#[test]
	fn map_retains_size() {
		let b1 = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2]);
		let b2 = b1.clone();

		assert_eq!(b1.len(), b2.map(|(_, _)| 5_u32).len());
	}

	#[test]
	fn map_maps_properly() {
		let b1: BoundedBTreeMap<u32, u32, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k * 2)).try_collect().unwrap();
		let b2: BoundedBTreeMap<u32, u32, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k)).try_collect().unwrap();

		assert_eq!(b1, b2.map(|(_, v)| v * 2));
	}

	#[test]
	fn try_map_retains_size() {
		let b1 = boundedmap_from_keys::<u32, ConstU32<7>>(&[1, 2]);
		let b2 = b1.clone();

		assert_eq!(b1.len(), b2.try_map::<_, (), _>(|(_, _)| Ok(5_u32)).unwrap().len());
	}

	#[test]
	fn try_map_maps_properly() {
		let b1: BoundedBTreeMap<u32, u32, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k * 2)).try_collect().unwrap();
		let b2: BoundedBTreeMap<u32, u32, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, k)).try_collect().unwrap();

		assert_eq!(b1, b2.try_map::<_, (), _>(|(_, v)| Ok(v * 2)).unwrap());
	}

	#[test]
	fn try_map_short_circuit() {
		let b1: BoundedBTreeMap<u8, u8, ConstU32<7>> = [1, 2, 3, 4].into_iter().map(|k| (k, k)).try_collect().unwrap();

		assert_eq!(Err("overflow"), b1.try_map(|(_, v)| v.checked_mul(100).ok_or("overflow")));
	}

	#[test]
	fn try_map_ok() {
		let b1: BoundedBTreeMap<u8, u8, ConstU32<7>> = [1, 2, 3, 4].into_iter().map(|k| (k, k)).try_collect().unwrap();
		let b2: BoundedBTreeMap<u8, u16, ConstU32<7>> =
			[1, 2, 3, 4].into_iter().map(|k| (k, (k as u16) * 100)).try_collect().unwrap();

		assert_eq!(Ok(b2), b1.try_map(|(_, v)| (v as u16).checked_mul(100_u16).ok_or("overflow")));
	}

	// Just a test that structs containing `BoundedBTreeMap` can derive `Hash`. (This was broken
	// when it was deriving `Hash`).
	#[test]
	#[cfg(feature = "std")]
	fn container_can_derive_hash() {
		#[derive(Hash)]
		struct Foo {
			bar: u8,
			map: BoundedBTreeMap<String, usize, ConstU32<16>>,
		}
	}
}