src/libcore/iter/range.rs

   1 // Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use convert::TryFrom;
  12 use mem;
  13 use ops::{self, Add, Sub};
  14 use usize;
  15
  16 use super::{FusedIterator, TrustedLen};
  17
  18 /// Objects that can be stepped over in both directions.
  19 ///
  20 /// The `steps_between` function provides a way to efficiently compare
  21 /// two `Step` objects.
  22 #[unstable(feature = "step_trait",
  23            reason = "likely to be replaced by finer-grained traits",
  24            issue = "42168")]
  25 pub trait Step: Clone + PartialOrd + Sized {
  26     /// Returns the number of steps between two step objects. The count is
  27     /// inclusive of `start` and exclusive of `end`.
  28     ///
  29     /// Returns `None` if it is not possible to calculate `steps_between`
  30     /// without overflow.
  31     fn steps_between(start: &Self, end: &Self) -> Option<usize>;
  32
  33     /// Replaces this step with `1`, returning itself
  34     fn replace_one(&mut self) -> Self;
  35
  36     /// Replaces this step with `0`, returning itself
  37     fn replace_zero(&mut self) -> Self;
  38
  39     /// Adds one to this step, returning the result
  40     fn add_one(&self) -> Self;
  41
  42     /// Subtracts one to this step, returning the result
  43     fn sub_one(&self) -> Self;
  44
  45     /// Add an usize, returning None on overflow
  46     fn add_usize(&self, n: usize) -> Option<Self>;
  47 }
  48
  49 // These are still macro-generated because the integer literals resolve to different types.
  50 macro_rules! step_identical_methods {
  51     () => {
  52         #[inline]
  53         fn replace_one(&mut self) -> Self {
  54             mem::replace(self, 1)
  55         }
  56
  57         #[inline]
  58         fn replace_zero(&mut self) -> Self {
  59             mem::replace(self, 0)
  60         }
  61
  62         #[inline]
  63         fn add_one(&self) -> Self {
  64             Add::add(*self, 1)
  65         }
  66
  67         #[inline]
  68         fn sub_one(&self) -> Self {
  69             Sub::sub(*self, 1)
  70         }
  71     }
  72 }
  73
  74 macro_rules! step_impl_unsigned {
  75     ($($t:ty)*) => ($(
  76         #[unstable(feature = "step_trait",
  77                    reason = "likely to be replaced by finer-grained traits",
  78                    issue = "42168")]
  79         impl Step for $t {
  80             #[inline]
  81             #[allow(trivial_numeric_casts)]
  82             fn steps_between(start: &$t, end: &$t) -> Option<usize> {
  83                 if *start < *end {
  84                     // Note: We assume $t <= usize here
  85                     Some((*end - *start) as usize)
  86                 } else {
  87                     Some(0)
  88                 }
  89             }
  90
  91             #[inline]
  92             #[allow(unreachable_patterns)]
  93             fn add_usize(&self, n: usize) -> Option<Self> {
  94                 match <$t>::try_from(n) {
  95                     Ok(n_as_t) => self.checked_add(n_as_t),
  96                     Err(_) => None,
  97                 }
  98             }
  99
 100             step_identical_methods!();
 101         }
 102     )*)
 103 }
 104 macro_rules! step_impl_signed {
 105     ($( [$t:ty : $unsigned:ty] )*) => ($(
 106         #[unstable(feature = "step_trait",
 107                    reason = "likely to be replaced by finer-grained traits",
 108                    issue = "42168")]
 109         impl Step for $t {
 110             #[inline]
 111             #[allow(trivial_numeric_casts)]
 112             fn steps_between(start: &$t, end: &$t) -> Option<usize> {
 113                 if *start < *end {
 114                     // Note: We assume $t <= isize here
 115                     // Use .wrapping_sub and cast to usize to compute the
 116                     // difference that may not fit inside the range of isize.
 117                     Some((*end as isize).wrapping_sub(*start as isize) as usize)
 118                 } else {
 119                     Some(0)
 120                 }
 121             }
 122
 123             #[inline]
 124             #[allow(unreachable_patterns)]
 125             fn add_usize(&self, n: usize) -> Option<Self> {
 126                 match <$unsigned>::try_from(n) {
 127                     Ok(n_as_unsigned) => {
 128                         // Wrapping in unsigned space handles cases like
 129                         // `-120_i8.add_usize(200) == Some(80_i8)`,
 130                         // even though 200_usize is out of range for i8.
 131                         let wrapped = (*self as $unsigned).wrapping_add(n_as_unsigned) as $t;
 132                         if wrapped >= *self {
 133                             Some(wrapped)
 134                         } else {
 135                             None  // Addition overflowed
 136                         }
 137                     }
 138                     Err(_) => None,
 139                 }
 140             }
 141
 142             step_identical_methods!();
 143         }
 144     )*)
 145 }
 146
 147 macro_rules! step_impl_no_between {
 148     ($($t:ty)*) => ($(
 149         #[unstable(feature = "step_trait",
 150                    reason = "likely to be replaced by finer-grained traits",
 151                    issue = "42168")]
 152         impl Step for $t {
 153             #[inline]
 154             fn steps_between(_start: &Self, _end: &Self) -> Option<usize> {
 155                 None
 156             }
 157
 158             #[inline]
 159             fn add_usize(&self, n: usize) -> Option<Self> {
 160                 self.checked_add(n as $t)
 161             }
 162
 163             step_identical_methods!();
 164         }
 165     )*)
 166 }
 167
 168 step_impl_unsigned!(usize u8 u16 u32);
 169 step_impl_signed!([isize: usize] [i8: u8] [i16: u16] [i32: u32]);
 170 #[cfg(target_pointer_width = "64")]
 171 step_impl_unsigned!(u64);
 172 #[cfg(target_pointer_width = "64")]
 173 step_impl_signed!([i64: u64]);
 174 // If the target pointer width is not 64-bits, we
 175 // assume here that it is less than 64-bits.
 176 #[cfg(not(target_pointer_width = "64"))]
 177 step_impl_no_between!(u64 i64);
 178 step_impl_no_between!(u128 i128);
 179
 180 macro_rules! range_exact_iter_impl {
 181     ($($t:ty)*) => ($(
 182         #[stable(feature = "rust1", since = "1.0.0")]
 183         impl ExactSizeIterator for ops::Range<$t> { }
 184     )*)
 185 }
 186
 187 macro_rules! range_incl_exact_iter_impl {
 188     ($($t:ty)*) => ($(
 189         #[unstable(feature = "inclusive_range",
 190                    reason = "recently added, follows RFC",
 191                    issue = "28237")]
 192         impl ExactSizeIterator for ops::RangeInclusive<$t> { }
 193     )*)
 194 }
 195
 196 macro_rules! range_trusted_len_impl {
 197     ($($t:ty)*) => ($(
 198         #[unstable(feature = "trusted_len", issue = "37572")]
 199         unsafe impl TrustedLen for ops::Range<$t> { }
 200     )*)
 201 }
 202
 203 macro_rules! range_incl_trusted_len_impl {
 204     ($($t:ty)*) => ($(
 205         #[unstable(feature = "inclusive_range",
 206                    reason = "recently added, follows RFC",
 207                    issue = "28237")]
 208         unsafe impl TrustedLen for ops::RangeInclusive<$t> { }
 209     )*)
 210 }
 211
 212 #[stable(feature = "rust1", since = "1.0.0")]
 213 impl<A: Step> Iterator for ops::Range<A> {
 214     type Item = A;
 215
 216     #[inline]
 217     fn next(&mut self) -> Option<A> {
 218         if self.start < self.end {
 219             // We check for overflow here, even though it can't actually
 220             // happen. Adding this check does however help llvm vectorize loops
 221             // for some ranges that don't get vectorized otherwise,
 222             // and this won't actually result in an extra check in an optimized build.
 223             if let Some(mut n) = self.start.add_usize(1) {
 224                 mem::swap(&mut n, &mut self.start);
 225                 Some(n)
 226             } else {
 227                 None
 228             }
 229         } else {
 230             None
 231         }
 232     }
 233
 234     #[inline]
 235     fn size_hint(&self) -> (usize, Option<usize>) {
 236         match Step::steps_between(&self.start, &self.end) {
 237             Some(hint) => (hint, Some(hint)),
 238             None => (0, None)
 239         }
 240     }
 241
 242     #[inline]
 243     fn nth(&mut self, n: usize) -> Option<A> {
 244         if let Some(plus_n) = self.start.add_usize(n) {
 245             if plus_n < self.end {
 246                 self.start = plus_n.add_one();
 247                 return Some(plus_n)
 248             }
 249         }
 250
 251         self.start = self.end.clone();
 252         None
 253     }
 254 }
 255
 256 // These macros generate `ExactSizeIterator` impls for various range types.
 257 // Range<{u,i}64> and RangeInclusive<{u,i}{32,64,size}> are excluded
 258 // because they cannot guarantee having a length <= usize::MAX, which is
 259 // required by ExactSizeIterator.
 260 range_exact_iter_impl!(usize u8 u16 u32 isize i8 i16 i32);
 261 range_incl_exact_iter_impl!(u8 u16 i8 i16);
 262
 263 // These macros generate `TrustedLen` impls.
 264 //
 265 // They need to guarantee that .size_hint() is either exact, or that
 266 // the upper bound is None when it does not fit the type limits.
 267 range_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 i64 u64);
 268 range_incl_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 i64 u64);
 269
 270 #[stable(feature = "rust1", since = "1.0.0")]
 271 impl<A: Step> DoubleEndedIterator for ops::Range<A> {
 272     #[inline]
 273     fn next_back(&mut self) -> Option<A> {
 274         if self.start < self.end {
 275             self.end = self.end.sub_one();
 276             Some(self.end.clone())
 277         } else {
 278             None
 279         }
 280     }
 281 }
 282
 283 #[unstable(feature = "fused", issue = "35602")]
 284 impl<A: Step> FusedIterator for ops::Range<A> {}
 285
 286 #[stable(feature = "rust1", since = "1.0.0")]
 287 impl<A: Step> Iterator for ops::RangeFrom<A> {
 288     type Item = A;
 289
 290     #[inline]
 291     fn next(&mut self) -> Option<A> {
 292         let mut n = self.start.add_one();
 293         mem::swap(&mut n, &mut self.start);
 294         Some(n)
 295     }
 296
 297     #[inline]
 298     fn size_hint(&self) -> (usize, Option<usize>) {
 299         (usize::MAX, None)
 300     }
 301
 302     #[inline]
 303     fn nth(&mut self, n: usize) -> Option<A> {
 304         let plus_n = self.start.add_usize(n).expect("overflow in RangeFrom::nth");
 305         self.start = plus_n.add_one();
 306         Some(plus_n)
 307     }
 308 }
 309
 310 #[unstable(feature = "fused", issue = "35602")]
 311 impl<A: Step> FusedIterator for ops::RangeFrom<A> {}
 312
 313 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 314 impl<A: Step> Iterator for ops::RangeInclusive<A> {
 315     type Item = A;
 316
 317     #[inline]
 318     fn next(&mut self) -> Option<A> {
 319         use cmp::Ordering::*;
 320
 321         match self.start.partial_cmp(&self.end) {
 322             Some(Less) => {
 323                 let n = self.start.add_one();
 324                 Some(mem::replace(&mut self.start, n))
 325             },
 326             Some(Equal) => {
 327                 let last = self.start.replace_one();
 328                 self.end.replace_zero();
 329                 Some(last)
 330             },
 331             _ => None,
 332         }
 333     }
 334
 335     #[inline]
 336     fn size_hint(&self) -> (usize, Option<usize>) {
 337         if !(self.start <= self.end) {
 338             return (0, Some(0));
 339         }
 340
 341         match Step::steps_between(&self.start, &self.end) {
 342             Some(hint) => (hint.saturating_add(1), hint.checked_add(1)),
 343             None => (0, None),
 344         }
 345     }
 346
 347     #[inline]
 348     fn nth(&mut self, n: usize) -> Option<A> {
 349         if let Some(plus_n) = self.start.add_usize(n) {
 350             use cmp::Ordering::*;
 351
 352             match plus_n.partial_cmp(&self.end) {
 353                 Some(Less) => {
 354                     self.start = plus_n.add_one();
 355                     return Some(plus_n)
 356                 }
 357                 Some(Equal) => {
 358                     self.start.replace_one();
 359                     self.end.replace_zero();
 360                     return Some(plus_n)
 361                 }
 362                 _ => {}
 363             }
 364         }
 365
 366         self.start.replace_one();
 367         self.end.replace_zero();
 368         None
 369     }
 370 }
 371
 372 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 373 impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
 374     #[inline]
 375     fn next_back(&mut self) -> Option<A> {
 376         use cmp::Ordering::*;
 377
 378         match self.start.partial_cmp(&self.end) {
 379             Some(Less) => {
 380                 let n = self.end.sub_one();
 381                 Some(mem::replace(&mut self.end, n))
 382             },
 383             Some(Equal) => {
 384                 let last = self.end.replace_zero();
 385                 self.start.replace_one();
 386                 Some(last)
 387             },
 388             _ => None,
 389         }
 390     }
 391 }
 392
 393 #[unstable(feature = "fused", issue = "35602")]
 394 impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}