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
use crate::fmt;
use crate::ops::Try;

use super::super::{Iterator, DoubleEndedIterator, FusedIterator};
use super::Map;

/// An iterator that maps each element to an iterator, and yields the elements
/// of the produced iterators.
///
/// This `struct` is created by the [`flat_map`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`flat_map`]: trait.Iterator.html#method.flat_map
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct FlatMap<I, U: IntoIterator, F> {
    inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>
}
impl<I: Iterator, U: IntoIterator, F: FnMut(I::Item) -> U> FlatMap<I, U, F> {
    pub(in super::super) fn new(iter: I, f: F) -> FlatMap<I, U, F> {
        FlatMap { inner: FlattenCompat::new(iter.map(f)) }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Clone, U, F: Clone> Clone for FlatMap<I, U, F>
where
    U: Clone + IntoIterator<IntoIter: Clone>,
{
    fn clone(&self) -> Self { FlatMap { inner: self.inner.clone() } }
}

#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<I: fmt::Debug, U, F> fmt::Debug for FlatMap<I, U, F>
where
    U: IntoIterator<IntoIter: fmt::Debug>,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("FlatMap").field("inner", &self.inner).finish()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
    where F: FnMut(I::Item) -> U,
{
    type Item = U::Item;

    #[inline]
    fn next(&mut self) -> Option<U::Item> { self.inner.next() }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }

    #[inline]
    fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        self.inner.try_fold(init, fold)
    }

    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.inner.fold(init, fold)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F>
where
    F: FnMut(I::Item) -> U,
    U: IntoIterator<IntoIter: DoubleEndedIterator>,
{
    #[inline]
    fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }

    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        self.inner.try_rfold(init, fold)
    }

    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.inner.rfold(init, fold)
    }
}

#[stable(feature = "fused", since = "1.26.0")]
impl<I, U, F> FusedIterator for FlatMap<I, U, F>
    where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}

/// An iterator that flattens one level of nesting in an iterator of things
/// that can be turned into iterators.
///
/// This `struct` is created by the [`flatten`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`flatten`]: trait.Iterator.html#method.flatten
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "iterator_flatten", since = "1.29.0")]
pub struct Flatten<I: Iterator<Item: IntoIterator>> {
    inner: FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>,
}

impl<I: Iterator<Item: IntoIterator>> Flatten<I> {
    pub(in super::super) fn new(iter: I) -> Flatten<I> {
        Flatten { inner: FlattenCompat::new(iter) }
    }
}

#[stable(feature = "iterator_flatten", since = "1.29.0")]
impl<I, U> fmt::Debug for Flatten<I>
where
    I: fmt::Debug + Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: fmt::Debug + Iterator,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Flatten").field("inner", &self.inner).finish()
    }
}

#[stable(feature = "iterator_flatten", since = "1.29.0")]
impl<I, U> Clone for Flatten<I>
where
    I: Clone + Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: Clone + Iterator,
{
    fn clone(&self) -> Self { Flatten { inner: self.inner.clone() } }
}

#[stable(feature = "iterator_flatten", since = "1.29.0")]
impl<I, U> Iterator for Flatten<I>
where
    I: Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: Iterator,
{
    type Item = U::Item;

    #[inline]
    fn next(&mut self) -> Option<U::Item> { self.inner.next() }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }

    #[inline]
    fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        self.inner.try_fold(init, fold)
    }

    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.inner.fold(init, fold)
    }
}

#[stable(feature = "iterator_flatten", since = "1.29.0")]
impl<I, U> DoubleEndedIterator for Flatten<I>
where
    I: DoubleEndedIterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: DoubleEndedIterator,
{
    #[inline]
    fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }

    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        self.inner.try_rfold(init, fold)
    }

    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        self.inner.rfold(init, fold)
    }
}

#[stable(feature = "iterator_flatten", since = "1.29.0")]
impl<I, U> FusedIterator for Flatten<I>
where
    I: FusedIterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: Iterator,
{}

/// Real logic of both `Flatten` and `FlatMap` which simply delegate to
/// this type.
#[derive(Clone, Debug)]
struct FlattenCompat<I, U> {
    iter: I,
    frontiter: Option<U>,
    backiter: Option<U>,
}
impl<I, U> FlattenCompat<I, U> {
    /// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
    fn new(iter: I) -> FlattenCompat<I, U> {
        FlattenCompat { iter, frontiter: None, backiter: None }
    }
}

impl<I, U> Iterator for FlattenCompat<I, U>
where
    I: Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: Iterator,
{
    type Item = U::Item;

    #[inline]
    fn next(&mut self) -> Option<U::Item> {
        loop {
            if let Some(ref mut inner) = self.frontiter {
                if let elt@Some(_) = inner.next() { return elt }
            }
            match self.iter.next() {
                None => return self.backiter.as_mut()?.next(),
                Some(inner) => self.frontiter = Some(inner.into_iter()),
            }
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let (flo, fhi) = self.frontiter.as_ref().map_or((0, Some(0)), U::size_hint);
        let (blo, bhi) = self.backiter.as_ref().map_or((0, Some(0)), U::size_hint);
        let lo = flo.saturating_add(blo);
        match (self.iter.size_hint(), fhi, bhi) {
            ((0, Some(0)), Some(a), Some(b)) => (lo, a.checked_add(b)),
            _ => (lo, None)
        }
    }

    #[inline]
    fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        #[inline]
        fn flatten<'a, T: IntoIterator, Acc, R: Try<Ok = Acc>>(
            frontiter: &'a mut Option<T::IntoIter>,
            fold: &'a mut impl FnMut(Acc, T::Item) -> R,
        ) -> impl FnMut(Acc, T) -> R + 'a {
            move |acc, x| {
                let mut mid = x.into_iter();
                let r = mid.try_fold(acc, &mut *fold);
                *frontiter = Some(mid);
                r
            }
        }

        if let Some(ref mut front) = self.frontiter {
            init = front.try_fold(init, &mut fold)?;
        }
        self.frontiter = None;

        init = self.iter.try_fold(init, flatten(&mut self.frontiter, &mut fold))?;
        self.frontiter = None;

        if let Some(ref mut back) = self.backiter {
            init = back.try_fold(init, &mut fold)?;
        }
        self.backiter = None;

        Try::from_ok(init)
    }

    #[inline]
    fn fold<Acc, Fold>(self, init: Acc, ref mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        #[inline]
        fn flatten<U: Iterator, Acc>(
            fold: &mut impl FnMut(Acc, U::Item) -> Acc,
        ) -> impl FnMut(Acc, U) -> Acc + '_ {
            move |acc, iter| iter.fold(acc, &mut *fold)
        }

        self.frontiter.into_iter()
            .chain(self.iter.map(IntoIterator::into_iter))
            .chain(self.backiter)
            .fold(init, flatten(fold))
    }
}

impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
where
    I: DoubleEndedIterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
    U: DoubleEndedIterator,
{
    #[inline]
    fn next_back(&mut self) -> Option<U::Item> {
        loop {
            if let Some(ref mut inner) = self.backiter {
                if let elt@Some(_) = inner.next_back() { return elt }
            }
            match self.iter.next_back() {
                None => return self.frontiter.as_mut()?.next_back(),
                next => self.backiter = next.map(IntoIterator::into_iter),
            }
        }
    }

    #[inline]
    fn try_rfold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
        Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
    {
        #[inline]
        fn flatten<'a, T: IntoIterator, Acc, R: Try<Ok = Acc>>(
            backiter: &'a mut Option<T::IntoIter>,
            fold: &'a mut impl FnMut(Acc, T::Item) -> R,
        ) -> impl FnMut(Acc, T) -> R + 'a where
            T::IntoIter: DoubleEndedIterator,
        {
            move |acc, x| {
                let mut mid = x.into_iter();
                let r = mid.try_rfold(acc, &mut *fold);
                *backiter = Some(mid);
                r
            }
        }

        if let Some(ref mut back) = self.backiter {
            init = back.try_rfold(init, &mut fold)?;
        }
        self.backiter = None;

        init = self.iter.try_rfold(init, flatten(&mut self.backiter, &mut fold))?;
        self.backiter = None;

        if let Some(ref mut front) = self.frontiter {
            init = front.try_rfold(init, &mut fold)?;
        }
        self.frontiter = None;

        Try::from_ok(init)
    }

    #[inline]
    fn rfold<Acc, Fold>(self, init: Acc, ref mut fold: Fold) -> Acc
        where Fold: FnMut(Acc, Self::Item) -> Acc,
    {
        #[inline]
        fn flatten<U: DoubleEndedIterator, Acc>(
            fold: &mut impl FnMut(Acc, U::Item) -> Acc,
        ) -> impl FnMut(Acc, U) -> Acc + '_ {
            move |acc, iter| iter.rfold(acc, &mut *fold)
        }

        self.frontiter.into_iter()
            .chain(self.iter.map(IntoIterator::into_iter))
            .chain(self.backiter)
            .rfold(init, flatten(fold))
    }
}