src/libcore/iter/traits.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 option::Option::{self, Some};
  12 use marker::Sized;
  13
  14 use super::Iterator;
  15
  16 /// Conversion from an `Iterator`.
  17 ///
  18 /// By implementing `FromIterator` for a type, you define how it will be
  19 /// created from an iterator. This is common for types which describe a
  20 /// collection of some kind.
  21 ///
  22 /// `FromIterator`'s [`from_iter()`] is rarely called explicitly, and is instead
  23 /// used through [`Iterator`]'s [`collect()`] method. See [`collect()`]'s
  24 /// documentation for more examples.
  25 ///
  26 /// [`from_iter()`]: #tymethod.from_iter
  27 /// [`Iterator`]: trait.Iterator.html
  28 /// [`collect()`]: trait.Iterator.html#method.collect
  29 ///
  30 /// See also: [`IntoIterator`].
  31 ///
  32 /// [`IntoIterator`]: trait.IntoIterator.html
  33 ///
  34 /// # Examples
  35 ///
  36 /// Basic usage:
  37 ///
  38 /// ```
  39 /// use std::iter::FromIterator;
  40 ///
  41 /// let five_fives = std::iter::repeat(5).take(5);
  42 ///
  43 /// let v = Vec::from_iter(five_fives);
  44 ///
  45 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
  46 /// ```
  47 ///
  48 /// Using [`collect()`] to implicitly use `FromIterator`:
  49 ///
  50 /// ```
  51 /// let five_fives = std::iter::repeat(5).take(5);
  52 ///
  53 /// let v: Vec<i32> = five_fives.collect();
  54 ///
  55 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
  56 /// ```
  57 ///
  58 /// Implementing `FromIterator` for your type:
  59 ///
  60 /// ```
  61 /// use std::iter::FromIterator;
  62 ///
  63 /// // A sample collection, that's just a wrapper over Vec<T>
  64 /// #[derive(Debug)]
  65 /// struct MyCollection(Vec<i32>);
  66 ///
  67 /// // Let's give it some methods so we can create one and add things
  68 /// // to it.
  69 /// impl MyCollection {
  70 ///     fn new() -> MyCollection {
  71 ///         MyCollection(Vec::new())
  72 ///     }
  73 ///
  74 ///     fn add(&mut self, elem: i32) {
  75 ///         self.0.push(elem);
  76 ///     }
  77 /// }
  78 ///
  79 /// // and we'll implement FromIterator
  80 /// impl FromIterator<i32> for MyCollection {
  81 ///     fn from_iter<I: IntoIterator<Item=i32>>(iter: I) -> Self {
  82 ///         let mut c = MyCollection::new();
  83 ///
  84 ///         for i in iter {
  85 ///             c.add(i);
  86 ///         }
  87 ///
  88 ///         c
  89 ///     }
  90 /// }
  91 ///
  92 /// // Now we can make a new iterator...
  93 /// let iter = (0..5).into_iter();
  94 ///
  95 /// // ... and make a MyCollection out of it
  96 /// let c = MyCollection::from_iter(iter);
  97 ///
  98 /// assert_eq!(c.0, vec![0, 1, 2, 3, 4]);
  99 ///
 100 /// // collect works too!
 101 ///
 102 /// let iter = (0..5).into_iter();
 103 /// let c: MyCollection = iter.collect();
 104 ///
 105 /// assert_eq!(c.0, vec![0, 1, 2, 3, 4]);
 106 /// ```
 107 #[stable(feature = "rust1", since = "1.0.0")]
 108 #[rustc_on_unimplemented="a collection of type `{Self}` cannot be \
 109                           built from an iterator over elements of type `{A}`"]
 110 pub trait FromIterator<A>: Sized {
 111     /// Creates a value from an iterator.
 112     ///
 113     /// See the [module-level documentation] for more.
 114     ///
 115     /// [module-level documentation]: trait.FromIterator.html
 116     ///
 117     /// # Examples
 118     ///
 119     /// Basic usage:
 120     ///
 121     /// ```
 122     /// use std::iter::FromIterator;
 123     ///
 124     /// let five_fives = std::iter::repeat(5).take(5);
 125     ///
 126     /// let v = Vec::from_iter(five_fives);
 127     ///
 128     /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
 129     /// ```
 130     #[stable(feature = "rust1", since = "1.0.0")]
 131     fn from_iter<T: IntoIterator<Item=A>>(iter: T) -> Self;
 132 }
 133
 134 /// Conversion into an `Iterator`.
 135 ///
 136 /// By implementing `IntoIterator` for a type, you define how it will be
 137 /// converted to an iterator. This is common for types which describe a
 138 /// collection of some kind.
 139 ///
 140 /// One benefit of implementing `IntoIterator` is that your type will [work
 141 /// with Rust's `for` loop syntax](index.html#for-loops-and-intoiterator).
 142 ///
 143 /// See also: [`FromIterator`].
 144 ///
 145 /// [`FromIterator`]: trait.FromIterator.html
 146 ///
 147 /// # Examples
 148 ///
 149 /// Basic usage:
 150 ///
 151 /// ```
 152 /// let v = vec![1, 2, 3];
 153 ///
 154 /// let mut iter = v.into_iter();
 155 ///
 156 /// let n = iter.next();
 157 /// assert_eq!(Some(1), n);
 158 ///
 159 /// let n = iter.next();
 160 /// assert_eq!(Some(2), n);
 161 ///
 162 /// let n = iter.next();
 163 /// assert_eq!(Some(3), n);
 164 ///
 165 /// let n = iter.next();
 166 /// assert_eq!(None, n);
 167 /// ```
 168 ///
 169 /// Implementing `IntoIterator` for your type:
 170 ///
 171 /// ```
 172 /// // A sample collection, that's just a wrapper over Vec<T>
 173 /// #[derive(Debug)]
 174 /// struct MyCollection(Vec<i32>);
 175 ///
 176 /// // Let's give it some methods so we can create one and add things
 177 /// // to it.
 178 /// impl MyCollection {
 179 ///     fn new() -> MyCollection {
 180 ///         MyCollection(Vec::new())
 181 ///     }
 182 ///
 183 ///     fn add(&mut self, elem: i32) {
 184 ///         self.0.push(elem);
 185 ///     }
 186 /// }
 187 ///
 188 /// // and we'll implement IntoIterator
 189 /// impl IntoIterator for MyCollection {
 190 ///     type Item = i32;
 191 ///     type IntoIter = ::std::vec::IntoIter<i32>;
 192 ///
 193 ///     fn into_iter(self) -> Self::IntoIter {
 194 ///         self.0.into_iter()
 195 ///     }
 196 /// }
 197 ///
 198 /// // Now we can make a new collection...
 199 /// let mut c = MyCollection::new();
 200 ///
 201 /// // ... add some stuff to it ...
 202 /// c.add(0);
 203 /// c.add(1);
 204 /// c.add(2);
 205 ///
 206 /// // ... and then turn it into an Iterator:
 207 /// for (i, n) in c.into_iter().enumerate() {
 208 ///     assert_eq!(i as i32, n);
 209 /// }
 210 /// ```
 211 #[stable(feature = "rust1", since = "1.0.0")]
 212 pub trait IntoIterator {
 213     /// The type of the elements being iterated over.
 214     #[stable(feature = "rust1", since = "1.0.0")]
 215     type Item;
 216
 217     /// Which kind of iterator are we turning this into?
 218     #[stable(feature = "rust1", since = "1.0.0")]
 219     type IntoIter: Iterator<Item=Self::Item>;
 220
 221     /// Creates an iterator from a value.
 222     ///
 223     /// See the [module-level documentation] for more.
 224     ///
 225     /// [module-level documentation]: trait.IntoIterator.html
 226     ///
 227     /// # Examples
 228     ///
 229     /// Basic usage:
 230     ///
 231     /// ```
 232     /// let v = vec![1, 2, 3];
 233     ///
 234     /// let mut iter = v.into_iter();
 235     ///
 236     /// let n = iter.next();
 237     /// assert_eq!(Some(1), n);
 238     ///
 239     /// let n = iter.next();
 240     /// assert_eq!(Some(2), n);
 241     ///
 242     /// let n = iter.next();
 243     /// assert_eq!(Some(3), n);
 244     ///
 245     /// let n = iter.next();
 246     /// assert_eq!(None, n);
 247     /// ```
 248     #[stable(feature = "rust1", since = "1.0.0")]
 249     fn into_iter(self) -> Self::IntoIter;
 250 }
 251
 252 #[stable(feature = "rust1", since = "1.0.0")]
 253 impl<I: Iterator> IntoIterator for I {
 254     type Item = I::Item;
 255     type IntoIter = I;
 256
 257     fn into_iter(self) -> I {
 258         self
 259     }
 260 }
 261
 262 /// Extend a collection with the contents of an iterator.
 263 ///
 264 /// Iterators produce a series of values, and collections can also be thought
 265 /// of as a series of values. The `Extend` trait bridges this gap, allowing you
 266 /// to extend a collection by including the contents of that iterator.
 267 ///
 268 /// # Examples
 269 ///
 270 /// Basic usage:
 271 ///
 272 /// ```
 273 /// // You can extend a String with some chars:
 274 /// let mut message = String::from("The first three letters are: ");
 275 ///
 276 /// message.extend(&['a', 'b', 'c']);
 277 ///
 278 /// assert_eq!("abc", &message[29..32]);
 279 /// ```
 280 ///
 281 /// Implementing `Extend`:
 282 ///
 283 /// ```
 284 /// // A sample collection, that's just a wrapper over Vec<T>
 285 /// #[derive(Debug)]
 286 /// struct MyCollection(Vec<i32>);
 287 ///
 288 /// // Let's give it some methods so we can create one and add things
 289 /// // to it.
 290 /// impl MyCollection {
 291 ///     fn new() -> MyCollection {
 292 ///         MyCollection(Vec::new())
 293 ///     }
 294 ///
 295 ///     fn add(&mut self, elem: i32) {
 296 ///         self.0.push(elem);
 297 ///     }
 298 /// }
 299 ///
 300 /// // since MyCollection has a list of i32s, we implement Extend for i32
 301 /// impl Extend<i32> for MyCollection {
 302 ///
 303 ///     // This is a bit simpler with the concrete type signature: we can call
 304 ///     // extend on anything which can be turned into an Iterator which gives
 305 ///     // us i32s. Because we need i32s to put into MyCollection.
 306 ///     fn extend<T: IntoIterator<Item=i32>>(&mut self, iter: T) {
 307 ///
 308 ///         // The implementation is very straightforward: loop through the
 309 ///         // iterator, and add() each element to ourselves.
 310 ///         for elem in iter {
 311 ///             self.add(elem);
 312 ///         }
 313 ///     }
 314 /// }
 315 ///
 316 /// let mut c = MyCollection::new();
 317 ///
 318 /// c.add(5);
 319 /// c.add(6);
 320 /// c.add(7);
 321 ///
 322 /// // let's extend our collection with three more numbers
 323 /// c.extend(vec![1, 2, 3]);
 324 ///
 325 /// // we've added these elements onto the end
 326 /// assert_eq!("MyCollection([5, 6, 7, 1, 2, 3])", format!("{:?}", c));
 327 /// ```
 328 #[stable(feature = "rust1", since = "1.0.0")]
 329 pub trait Extend<A> {
 330     /// Extends a collection with the contents of an iterator.
 331     ///
 332     /// As this is the only method for this trait, the [trait-level] docs
 333     /// contain more details.
 334     ///
 335     /// [trait-level]: trait.Extend.html
 336     ///
 337     /// # Examples
 338     ///
 339     /// Basic usage:
 340     ///
 341     /// ```
 342     /// // You can extend a String with some chars:
 343     /// let mut message = String::from("abc");
 344     ///
 345     /// message.extend(['d', 'e', 'f'].iter());
 346     ///
 347     /// assert_eq!("abcdef", &message);
 348     /// ```
 349     #[stable(feature = "rust1", since = "1.0.0")]
 350     fn extend<T: IntoIterator<Item=A>>(&mut self, iter: T);
 351 }
 352
 353 /// An iterator able to yield elements from both ends.
 354 ///
 355 /// Something that implements `DoubleEndedIterator` has one extra capability
 356 /// over something that implements [`Iterator`]: the ability to also take
 357 /// `Item`s from the back, as well as the front.
 358 ///
 359 /// It is important to note that both back and forth work on the same range,
 360 /// and do not cross: iteration is over when they meet in the middle.
 361 ///
 362 /// In a similar fashion to the [`Iterator`] protocol, once a
 363 /// `DoubleEndedIterator` returns `None` from a `next_back()`, calling it again
 364 /// may or may not ever return `Some` again. `next()` and `next_back()` are
 365 /// interchangable for this purpose.
 366 ///
 367 /// [`Iterator`]: trait.Iterator.html
 368 ///
 369 /// # Examples
 370 ///
 371 /// Basic usage:
 372 ///
 373 /// ```
 374 /// let numbers = vec![1, 2, 3, 4, 5, 6];
 375 ///
 376 /// let mut iter = numbers.iter();
 377 ///
 378 /// assert_eq!(Some(&1), iter.next());
 379 /// assert_eq!(Some(&6), iter.next_back());
 380 /// assert_eq!(Some(&5), iter.next_back());
 381 /// assert_eq!(Some(&2), iter.next());
 382 /// assert_eq!(Some(&3), iter.next());
 383 /// assert_eq!(Some(&4), iter.next());
 384 /// assert_eq!(None, iter.next());
 385 /// assert_eq!(None, iter.next_back());
 386 /// ```
 387 #[stable(feature = "rust1", since = "1.0.0")]
 388 pub trait DoubleEndedIterator: Iterator {
 389     /// Removes and returns an element from the end of the iterator.
 390     ///
 391     /// Returns `None` when there are no more elements.
 392     ///
 393     /// The [trait-level] docs contain more details.
 394     ///
 395     /// [trait-level]: trait.DoubleEndedIterator.html
 396     ///
 397     /// # Examples
 398     ///
 399     /// Basic usage:
 400     ///
 401     /// ```
 402     /// let numbers = vec![1, 2, 3, 4, 5, 6];
 403     ///
 404     /// let mut iter = numbers.iter();
 405     ///
 406     /// assert_eq!(Some(&1), iter.next());
 407     /// assert_eq!(Some(&6), iter.next_back());
 408     /// assert_eq!(Some(&5), iter.next_back());
 409     /// assert_eq!(Some(&2), iter.next());
 410     /// assert_eq!(Some(&3), iter.next());
 411     /// assert_eq!(Some(&4), iter.next());
 412     /// assert_eq!(None, iter.next());
 413     /// assert_eq!(None, iter.next_back());
 414     /// ```
 415     #[stable(feature = "rust1", since = "1.0.0")]
 416     fn next_back(&mut self) -> Option<Self::Item>;
 417 }
 418
 419 #[stable(feature = "rust1", since = "1.0.0")]
 420 impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for &'a mut I {
 421     fn next_back(&mut self) -> Option<I::Item> { (**self).next_back() }
 422 }
 423
 424 /// An iterator that knows its exact length.
 425 ///
 426 /// Many [`Iterator`]s don't know how many times they will iterate, but some do.
 427 /// If an iterator knows how many times it can iterate, providing access to
 428 /// that information can be useful. For example, if you want to iterate
 429 /// backwards, a good start is to know where the end is.
 430 ///
 431 /// When implementing an `ExactSizeIterator`, You must also implement
 432 /// [`Iterator`]. When doing so, the implementation of [`size_hint()`] *must*
 433 /// return the exact size of the iterator.
 434 ///
 435 /// [`Iterator`]: trait.Iterator.html
 436 /// [`size_hint()`]: trait.Iterator.html#method.size_hint
 437 ///
 438 /// The [`len()`] method has a default implementation, so you usually shouldn't
 439 /// implement it. However, you may be able to provide a more performant
 440 /// implementation than the default, so overriding it in this case makes sense.
 441 ///
 442 /// [`len()`]: #method.len
 443 ///
 444 /// # Examples
 445 ///
 446 /// Basic usage:
 447 ///
 448 /// ```
 449 /// // a finite range knows exactly how many times it will iterate
 450 /// let five = 0..5;
 451 ///
 452 /// assert_eq!(5, five.len());
 453 /// ```
 454 ///
 455 /// In the [module level docs][moddocs], we implemented an [`Iterator`],
 456 /// `Counter`. Let's implement `ExactSizeIterator` for it as well:
 457 ///
 458 /// [moddocs]: index.html
 459 ///
 460 /// ```
 461 /// # struct Counter {
 462 /// #     count: usize,
 463 /// # }
 464 /// # impl Counter {
 465 /// #     fn new() -> Counter {
 466 /// #         Counter { count: 0 }
 467 /// #     }
 468 /// # }
 469 /// # impl Iterator for Counter {
 470 /// #     type Item = usize;
 471 /// #     fn next(&mut self) -> Option<usize> {
 472 /// #         self.count += 1;
 473 /// #         if self.count < 6 {
 474 /// #             Some(self.count)
 475 /// #         } else {
 476 /// #             None
 477 /// #         }
 478 /// #     }
 479 /// # }
 480 /// impl ExactSizeIterator for Counter {
 481 ///     // We already have the number of iterations, so we can use it directly.
 482 ///     fn len(&self) -> usize {
 483 ///         self.count
 484 ///     }
 485 /// }
 486 ///
 487 /// // And now we can use it!
 488 ///
 489 /// let counter = Counter::new();
 490 ///
 491 /// assert_eq!(0, counter.len());
 492 /// ```
 493 #[stable(feature = "rust1", since = "1.0.0")]
 494 pub trait ExactSizeIterator: Iterator {
 495     /// Returns the exact number of times the iterator will iterate.
 496     ///
 497     /// This method has a default implementation, so you usually should not
 498     /// implement it directly. However, if you can provide a more efficient
 499     /// implementation, you can do so. See the [trait-level] docs for an
 500     /// example.
 501     ///
 502     /// This function has the same safety guarantees as the [`size_hint()`]
 503     /// function.
 504     ///
 505     /// [trait-level]: trait.ExactSizeIterator.html
 506     /// [`size_hint()`]: trait.Iterator.html#method.size_hint
 507     ///
 508     /// # Examples
 509     ///
 510     /// Basic usage:
 511     ///
 512     /// ```
 513     /// // a finite range knows exactly how many times it will iterate
 514     /// let five = 0..5;
 515     ///
 516     /// assert_eq!(5, five.len());
 517     /// ```
 518     #[inline]
 519     #[stable(feature = "rust1", since = "1.0.0")]
 520     fn len(&self) -> usize {
 521         let (lower, upper) = self.size_hint();
 522         // Note: This assertion is overly defensive, but it checks the invariant
 523         // guaranteed by the trait. If this trait were rust-internal,
 524         // we could use debug_assert!; assert_eq! will check all Rust user
 525         // implementations too.
 526         assert_eq!(upper, Some(lower));
 527         lower
 528     }
 529
 530     /// Returns whether the iterator is empty.
 531     ///
 532     /// This method has a default implementation using `self.len()`, so you
 533     /// don't need to implement it yourself.
 534     ///
 535     /// # Examples
 536     ///
 537     /// Basic usage:
 538     ///
 539     /// ```
 540     /// #![feature(exact_size_is_empty)]
 541     ///
 542     /// let mut one_element = 0..1;
 543     /// assert!(!one_element.is_empty());
 544     ///
 545     /// assert_eq!(one_element.next(), Some(0));
 546     /// assert!(one_element.is_empty());
 547     ///
 548     /// assert_eq!(one_element.next(), None);
 549     /// ```
 550     #[inline]
 551     #[unstable(feature = "exact_size_is_empty", issue = "35428")]
 552     fn is_empty(&self) -> bool {
 553         self.len() == 0
 554     }
 555 }
 556
 557 #[stable(feature = "rust1", since = "1.0.0")]
 558 impl<'a, I: ExactSizeIterator + ?Sized> ExactSizeIterator for &'a mut I {}
 559
 560 /// Trait to represent types that can be created by summing up an iterator.
 561 ///
 562 /// This trait is used to implement the `sum` method on iterators. Types which
 563 /// implement the trait can be generated by the `sum` method. Like
 564 /// `FromIterator` this trait should rarely be called directly and instead
 565 /// interacted with through `Iterator::sum`.
 566 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 567 pub trait Sum<A = Self>: Sized {
 568     /// Method which takes an iterator and generates `Self` from the elements by
 569     /// "summing up" the items.
 570     #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 571     fn sum<I: Iterator<Item=A>>(iter: I) -> Self;
 572 }
 573
 574 /// Trait to represent types that can be created by multiplying elements of an
 575 /// iterator.
 576 ///
 577 /// This trait is used to implement the `product` method on iterators. Types
 578 /// which implement the trait can be generated by the `product` method. Like
 579 /// `FromIterator` this trait should rarely be called directly and instead
 580 /// interacted with through `Iterator::product`.
 581 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 582 pub trait Product<A = Self>: Sized {
 583     /// Method which takes an iterator and generates `Self` from the elements by
 584     /// multiplying the items.
 585     #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 586     fn product<I: Iterator<Item=A>>(iter: I) -> Self;
 587 }
 588
 589 macro_rules! integer_sum_product {
 590     ($($a:ident)*) => ($(
 591         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 592         impl Sum for $a {
 593             fn sum<I: Iterator<Item=$a>>(iter: I) -> $a {
 594                 iter.fold(0, |a, b| {
 595                     a.checked_add(b).expect("overflow in sum")
 596                 })
 597             }
 598         }
 599
 600         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 601         impl Product for $a {
 602             fn product<I: Iterator<Item=$a>>(iter: I) -> $a {
 603                 iter.fold(1, |a, b| {
 604                     a.checked_mul(b).expect("overflow in product")
 605                 })
 606             }
 607         }
 608
 609         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 610         impl<'a> Sum<&'a $a> for $a {
 611             fn sum<I: Iterator<Item=&'a $a>>(iter: I) -> $a {
 612                 iter.fold(0, |a, b| {
 613                     a.checked_add(*b).expect("overflow in sum")
 614                 })
 615             }
 616         }
 617
 618         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 619         impl<'a> Product<&'a $a> for $a {
 620             fn product<I: Iterator<Item=&'a $a>>(iter: I) -> $a {
 621                 iter.fold(1, |a, b| {
 622                     a.checked_mul(*b).expect("overflow in product")
 623                 })
 624             }
 625         }
 626     )*)
 627 }
 628
 629 macro_rules! float_sum_product {
 630     ($($a:ident)*) => ($(
 631         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 632         impl Sum for $a {
 633             fn sum<I: Iterator<Item=$a>>(iter: I) -> $a {
 634                 iter.fold(0.0, |a, b| a + b)
 635             }
 636         }
 637
 638         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 639         impl Product for $a {
 640             fn product<I: Iterator<Item=$a>>(iter: I) -> $a {
 641                 iter.fold(1.0, |a, b| a * b)
 642             }
 643         }
 644
 645         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 646         impl<'a> Sum<&'a $a> for $a {
 647             fn sum<I: Iterator<Item=&'a $a>>(iter: I) -> $a {
 648                 iter.fold(0.0, |a, b| a + *b)
 649             }
 650         }
 651
 652         #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 653         impl<'a> Product<&'a $a> for $a {
 654             fn product<I: Iterator<Item=&'a $a>>(iter: I) -> $a {
 655                 iter.fold(1.0, |a, b| a * *b)
 656             }
 657         }
 658     )*)
 659 }
 660
 661 integer_sum_product! { i8 i16 i32 i64 isize u8 u16 u32 u64 usize }
 662 float_sum_product! { f32 f64 }