// * [Part 06: Copy, Lifetimes](part06.html)
// * [Part 07: Operator Overloading, Tests, Formating](part07.html)
// * [Part 08: Associated Types, Modules](part08.html)
+// * [Part 09: Iterators](part08.html)
// * (to be continued)
#![allow(dead_code, unused_imports, unused_variables, unused_mut)]
mod part00;
//@ specifying its type parameter doesn't tell us all that much.
fn read_vec() -> Vec<i32> {
let mut vec: Vec<i32> = Vec::<i32>::new();
- // The central handle to the standard input is made available by `io::stdin()`.
+ // The central handle to the standard input is made available by the function `io::stdin`.
let stdin = io::stdin();
println!("Enter a list of numbers, one per line. End with Ctrl-D.");
//@ We would now like to iterate over standard input line-by-line. We can use a `for` loop
//@ for that, but there is a catch: What happens if there is some other piece of code running
//@ concurrently, that also reads from standard input? The result would be a mess. Hence
- //@ Rust requires us to `lock()` standard input if we want to perform large operations on
+ //@ Rust requires us to `lock` standard input if we want to perform large operations on
//@ it. (See [the documentation](http://doc.rust-lang.org/stable/std/io/struct.Stdin.html) for more
//@ details.)
for line in stdin.lock().lines() {
//@ You will see that `io::Result` is actually just an alias for `Result`, so click on that to obtain
//@ the list of all constructors and methods of the type.
- //@ We will be lazy here and just assume that nothing goes wrong: `unwrap()` returns the `String` if there is one,
+ //@ We will be lazy here and just assume that nothing goes wrong: `unwrap` returns the `String` if there is one,
//@ and panics the program otherwise. Since a `Result` carries some details about the error that occurred,
//@ there will be a somewhat reasonable error message. Still, you would not want a user to see such
//@ an error, so in a "real" program, we would have to do proper error handling.
- //@ Can you find the documentation of `Result::unwrap()`?
+ //@ Can you find the documentation of `Result::unwrap`?
//@
// I chose the same name (`line`) for the new variable to ensure that I will never, accidentally,
// access the "old" `line` again.
let line = line.unwrap();
// Now that we have our `String`, we want to make it an `i32`.
- //@ We first `trim()` the `line` to remove leading and trailing whitespace.
+ //@ We first `trim` the `line` to remove leading and trailing whitespace.
//@ `parse` is a method on `String` that can convert a string to anything. Try finding it's documentation!
//@ In this case, Rust *could* figure out automatically that we need an `i32` (because of the return type
//@ something that is not a number).
//@ This is a common pattern in Rust: Operations that could go wrong will return `Option` or `Result`.
//@ The only way to get to the value we are interested in is through pattern matching (and through helper functions
- //@ like `unwrap()`). If we call a function that returns a `Result`, and throw the return value away,
+ //@ like `unwrap`). If we call a function that returns a `Result`, and throw the return value away,
//@ the compiler will emit a warning. It is hence impossible for us to *forget* handling an error,
//@ or to accidentally use a value that doesn't make any sense because there was an error producing it.
Ok(num) => {
//@ `data` public - otherwise, the next parts of this course could not work on `BigInt`s. Of course, in a
//@ real program, one would make the field private to ensure that the invariant (no trailing zeros) is maintained.
pub struct BigInt {
- pub data: Vec<u64>,
+ pub data: Vec<u64>, // least significant digit first, no trailing zeros
}
// Now that we fixed the data representation, we can start implementing methods on it.
//@ fields and initial values assigned to them.
pub fn new(x: u64) -> Self {
if x == 0 {
- BigInt { data: vec![] }
+ BigInt { data: vec![] } /*@*/
} else {
BigInt { data: vec![x] } /*@*/
}
//
// **Exercise 05.1**: Implement this function.
//
- // *Hint*: You can use `pop()` to remove the last element of a vector.
+ // *Hint*: You can use `pop` to remove the last element of a vector.
pub fn from_vec(mut v: Vec<u64>) -> Self {
unimplemented!()
}
}
// Now we can write `vec_min`.
-//@ However, in order to make it type-check, we have to make a full (deep) copy of e by calling `clone()`.
+//@ However, in order to make it type-check, we have to make a full (deep) copy of e by calling `clone`.
fn vec_min(v: &Vec<BigInt>) -> Option<BigInt> {
let mut min: Option<BigInt> = None;
for e in v {
//@ `e.clone()`, Rust will complain "Cannot move out of borrowed content". That's because
//@ `e` is a `&BigInt`. Assigning `min = Some(*e)` works just like a function call: Ownership of the
//@ underlying data is transferred from where `e` borrows from to `min`. But that's not allowed, since
-//@ we just borrowed `e`, so we cannot empty it! We can, however, call `clone()` on it. Then we own
+//@ we just borrowed `e`, so we cannot empty it! We can, however, call `clone` on it. Then we own
//@ the copy that was created, and hence we can store it in `min`. <br/>
//@ Of course, making such a full copy is expensive, so we'd like to avoid it. We'll some to that in the next part.
//@ `Clone`. This makes the cost explicit.
// ## Lifetimes
-//@ To fix the performance problems of `vec_min`, we need to avoid using `clone()`. We'd like
+//@ To fix the performance problems of `vec_min`, we need to avoid using `clone`. We'd like
//@ the return value to not be owned (remember that this was the source of our need for cloning), but *borrowed*.
//@ The function `head` demonstrates how that could work: It borrows the first element of a vector if it is non-empty.
// **Exercise 08.6**: Write a subtraction function, and testcases for it. Decide for yourself how you want to handle negative results.
// For example, you may want to return an `Option`, to panic, or to return `0`.
-//@ [index](main.html) | [previous](part07.html) | [next](main.html)
+//@ [index](main.html) | [previous](part07.html) | [next](part09.html)
-// Rust-101, Part 09: Iterators (WIP)
-// ==================================
+// Rust-101, Part 09: Iterators
+// ============================
use part05::BigInt;
-// In the following, we will look into the iterator mechanism of Rust and make our `BigInt` compatible
-// with the `for` loops. Of course, this is all about implementing particular traits again. In particular,
-// an iterator is something that implements the `Iterator` trait. As you can see in [the documentation](http://doc.rust-lang.org/beta/std/iter/trait.Iterator.html),
-// this trait mandates a single function `next` returning an `Option<Self::Item>`, where `Item` is an
-// associated type chosen by the implementation. (There are many more methods provided for `Iterator`,
-// but they all have default implementations, so we don't have to worry about them right now).
-//
-// For the case of `BigInt`, we want our iterator to iterate over the digits in normal, notational order: The most-significant
-// digit comes first. So, we have to write down some type, and implement `Iterator` for it such that `next` returns the digits
-// one-by-one. Clearly, the iterator must somehow be able to access the number it iterates over, and it must store its current
-// location. However, it cannot *own* the `BigInt`, because then the number would be gone after iteration! That'd certainly be bad.
-// The only alternative is for the iterator to *borrow* the number.
+//@ In the following, we will look into the iterator mechanism of Rust and make our `BigInt` compatible
+//@ with the `for` loops. Of course, this is all about implementing certain traits again. In particular,
+//@ an iterator is something that implements the `Iterator` trait. As you can see in [the documentation](http://doc.rust-lang.org/beta/std/iter/trait.Iterator.html),
+//@ this trait mandates a single function `next` returning an `Option<Self::Item>`, where `Item` is an
+//@ associated type chosen by the implementation. (There are many more methods provided for `Iterator`,
+//@ but they all have default implementations, so we don't have to worry about them right now.)
+//@
+//@ For the case of `BigInt`, we want our iterator to iterate over the digits in normal, notational order: The most-significant
+//@ digit comes first. So, we have to write down some type, and implement `Iterator` for it such that `next` returns the digits
+//@ one-by-one. Clearly, the iterator must somehow be able to access the number it iterates over, and it must store its current
+//@ location. However, it cannot *own* the `BigInt`, because then the number would be gone after iteration! That'd certainly be bad.
+//@ The only alternative is for the iterator to *borrow* the number.
-// In writing this down, we again have to be explicit about the lifetime of the borrow: We can't just have an
-// `Iter`, we must have an `Iter<'a>` that borrowed the number for lifetime `'a`. This is our first example of
-// a datatype that's polymorphic in a lifetime, as opposed to a type. <br/>
-// `usize` here is the type of unsigned, pointer-sized numbers. It is typically the type of "lengths of things",
-// in particular, it is the type of the length of a `Vec` and hence the right type to store an offset into the vector of digits.
-struct Iter<'a> {
+//@ In writing this down, we again have to be explicit about the lifetime of the borrow: We can't just have an
+//@ `Iter`, we must have an `Iter<'a>` that borrows the number for lifetime `'a`. This is our first example of
+//@ a data-type that's polymorphic in a lifetime, as opposed to a type. <br/>
+//@ `usize` here is the type of unsigned, pointer-sized numbers. It is typically the type of "lengths of things",
+//@ in particular, it is the type of the length of a `Vec` and hence the right type to store an offset into the vector of digits.
+pub struct Iter<'a> {
num: &'a BigInt,
idx: usize, // the index of the last number that was returned
}
fn next(&mut self) -> Option<u64> {
// First, check whether there's any more digits to return.
if self.idx == 0 {
- // We already returned all the digits.
+ // We already returned all the digits, nothing to do.
None /*@*/
} else {
- // Decrement, and return next digit.
+ // Otherwise: Decrement, and return next digit.
self.idx = self.idx - 1; /*@*/
Some(self.num.data[self.idx]) /*@*/
}
// All we need now is a function that creates such an iterator for a given `BigInt`.
impl BigInt {
- // Notice that when we write the type of `iter`, we don't actually have to give the lifetime parameter of `Iter`. Just as it is
- // the case with functions returning borrowed data, you can elide the lifetime. The rules for adding the lifetimes are exactly the
- // same. (See the last section of [part 06](part06.html).)
+ //@ Notice that when we write the type of `iter`, we don't actually have to give the lifetime parameter of `Iter`. Just as it is
+ //@ the case with functions returning borrowed data, you can elide the lifetime. The rules for adding the lifetimes are exactly the
+ //@ same. (See the last section of [part 06](part06.html).)
fn iter(&self) -> Iter {
Iter { num: self, idx: self.data.len() } /*@*/
}
// Of course, we don't have to use `for` to apply the iterator. We can also explicitly call `next`.
fn print_digits_v1(b: &BigInt) {
let mut iter = b.iter();
- // `loop` is the keyword for a loop without a condition: It runs endlessly, or until you break out of
- // it with `break` or `return`.
+ //@ `loop` is the keyword for a loop without a condition: It runs endlessly, or until you break out of
+ //@ it with `break` or `return`.
loop {
// Each time we go through the loop, we analyze the next element presented by the iterator - until it stops.
- match iter.next() {
- None => break,
- Some(digit) => println!("{}", digit)
- }
+ match iter.next() { /*@*/
+ None => break, /*@*/
+ Some(digit) => println!("{}", digit) /*@*/
+ } /*@*/
}
}
-// Now, it turns out that this combination of doing a loop and a pattern matching is fairly common, and Rust
-// provides some convenient syntactic sugar for it.
+//@ Now, it turns out that this combination of doing a loop and a pattern matching is fairly common, and Rust
+//@ provides some convenient syntactic sugar for it.
fn print_digits_v2(b: &BigInt) {
let mut iter = b.iter();
- // `while let` performs the given pattern matching on every round of the loop, and cancels the loop if the pattern
- // doesn't match. There's also `if let`, which works similar, but of course without the loopy part.
+ //@ `while let` performs the given pattern matching on every round of the loop, and cancels the loop if the pattern
+ //@ doesn't match. There's also `if let`, which works similar, but of course without the loopy part.
while let Some(digit) = iter.next() {
println!("{}", digit)
}
}
-// ## Iterator invalidation and lifetimes
-// You may have been surprised that we had to explicitly annotate a lifetime when we wrote `Iter`. Of
-// course, with lifetimes being present at every borrow in Rust, this is only consistent. But do we at
-// least gain something from this extra annotation burden? (Thankfully, this burden only occurs when we
-// define *types*, and not when we define functions - which is typically much more common.)
+// **Exercise 09.1**: Write a testcase for the iterator, making sure it yields the corrects numbers.
//
-// It turns out that the answer to this question is yes! This particular aspect of the concept of
-// lifetimes helps Rust to eliminate the issue of *iterator invalidation*. Consider the following
-// piece of code.
+// **Exercise 09.2**: Write a function `iter_ldf` that iterators over the digits with the least-significant
+// digits coming first. Write a testcase for it.
+
+// ## Iterator invalidation and lifetimes
+//@ You may have been surprised that we had to explicitly annotate a lifetime when we wrote `Iter`. Of
+//@ course, with lifetimes being present at every borrow in Rust, this is only consistent. But do we at
+//@ least gain something from this extra annotation burden? (Thankfully, this burden only occurs when we
+//@ define *types*, and not when we define functions - which is typically much more common.)
+
+//@ It turns out that the answer to this question is yes! This particular aspect of the concept of
+//@ lifetimes helps Rust to eliminate the issue of *iterator invalidation*. Consider the following
+//@ piece of code.
fn iter_invalidation_demo() {
let mut b = BigInt::new(1 << 63) + BigInt::new(1 << 16) + BigInt::new(1 << 63);
for digit in b.iter() {
/*b = b + BigInt::new(1);*/ /* BAD! */
}
}
-// If you enable the bad line, Rust will reject the code. Why? The problem is that we are modifying the
-// number while iterating over it. In other languages, this can have all sorts of effects from inconsistent
-// data or throwing an exception (Java) to bad pointers being dereferenced (C++). Rust, however, is able to
-// detect this situation. When you call `iter`, you have to borrow `b` for some lifetime `'a`, and you obtain
-// `Iter<'a>`. This is an iterator that's only valid for lifetime `'a`. Gladly, we have this annotation available
-// to make such a statement. Now, since we are using the iterator throughout the loop, `'a` has to span the loop.
-// This `b` is borrowed for the duration of the loop, and we cannot mutate it. This is yet another example for
-// how the combination of mutation and aliasing leads to undesired effects (not necessarily crashes, like in Java),
-// which Rust successfully prevents.
-//
-// Technically speaking, there's one more subtlety that I did not explain yet. We never explicitly tied the lifetime `'a` of the
-// iterator to the loop so how does this happen? The answer lies in the full type of `next()`:
-// `fn<'a, 'b>(&'b mut Iter<'a>) -> Option<u64>`. Since `next()` takes a *borrowed* iterator, there are two lifetimes involved:
-// The lifetime of the borrow of the iterator, and the lifetime of the iterator itself. In such a case of nested lifetimes,
-// Rust implicitly adds the additional constraint that the inner lifetime *outlives* the outer one: The borrow of an iterator
-// cannot be valid for longer than the iterator itself is valid. This means that the lifetime `'a` of the iterator needs
-// to outlive every call to `next()`, and hence the loop. Lucky enough, this all happens without our intervention.
+//@ If you enable the bad line, Rust will reject the code. Why? The problem is that we are modifying the
+//@ number while iterating over it. In other languages, this can have all sorts of effects from inconsistent
+//@ data or throwing an exception (Java) to bad pointers being dereferenced (C++). Rust, however, is able to
+//@ detect this situation. When you call `iter`, you have to borrow `b` for some lifetime `'a`, and you obtain
+//@ `Iter<'a>`. This is an iterator that's only valid for lifetime `'a`. Gladly, we have this annotation available
+//@ to make such a statement. Rust enforces that `'a` spans every call to `next`, which means it has to span the loop.
+//@ Thus `b` is borrowed for the duration of the loop, and we cannot mutate it. This is yet another example for
+//@ how the combination of mutation and aliasing leads to undesired effects (not necessarily crashes, think of Java),
+//@ which Rust successfully prevents.
+
+// ## Iterator conversion trait
+//@ If you closely compare the `for` loop in `main` above, with the one in `vec_min`, you will notice that we were able to write
+//@ `for e in v` earlier, but now we have to call `iter`. Why is that? Well, the `for` sugar is not actually tied to `Iterator`.
+//@ Instead, if demands an implementation of [`IntoIterator`](http://doc.rust-lang.org/beta/std/iter/trait.IntoIterator.html).
+//@ That's a trait of types that provide a *conversion* function into some kind of iterator. These conversion traits are a frequent
+//@ pattern in Rust: Rather than demanding that something is an iterator, or a string, or whatever; one demands that something
+//@ can be converted to an iterator/string/whatever. This provides convenience similar to overloading of functions: The function
+//@ can be called with lots of different types. By implementing such traits for your types, you can even make your own types
+//@ work smoothly with existing library functions. As usually for Rust, this abstraction comes at zero cost: If your data is already
+//@ of the right type, the conversion function will not do anything and trivially be optimized away.
+//@ If you have a look at the documentation of `IntoIterator`, you will notice that the function `into_iter` it provides actually
+//@ consumes its argument. So, we'd like to make `Self` a borrowed type, such that the number is not lost after the iteration.
+impl<'a> IntoIterator for &'a BigInt {
+ type Item = u64;
+ type IntoIter = Iter<'a>;
+ fn into_iter(self) -> Iter<'a> {
+ self.iter()
+ }
+}
+// With this in place, you can now replace `b.iter()` in `main` by `&b`. Go ahead and try it! <br/>
+//@ Wait, `&b`? Why that? Well, we implemented `IntoIterator` for `&BigInt`, so we have to borrow `b`. If we wanted to be able to write
+//@ just `b`, we'd have to also implement `IntoIterator` for `BigInt` - which, as already mentioned, would mean that `b` is actually consumed
+//@ by the iteration, and gone. This can easily happen, for example, with a `Vec`: Both `Vec` and `&Vec` implement `IntoIterator`, so if
+//@ you do `for e in v`, and `v` has type `Vec`, then you will obtain ownership of the elements during the iteration - and destroy the vector
+//@ in the process. We actually did that in `vec_min`, but we did not care. You can write `for e in &v` or `for e in v.iter()` to avoid this.
//@ [index](main.html) | [previous](part08.html) | [next](main.html)
mod part06;
mod part07;
mod part08;
+mod part09;
// This decides which part is actually run.
fn main() {
fn read_vec() -> Vec<i32> {
let mut vec: Vec<i32> = Vec::<i32>::new();
- // The central handle to the standard input is made available by `io::stdin()`.
+ // The central handle to the standard input is made available by the function `io::stdin`.
let stdin = io::stdin();
println!("Enter a list of numbers, one per line. End with Ctrl-D.");
for line in stdin.lock().lines() {
// ## Big Numbers
pub struct BigInt {
- pub data: Vec<u64>,
+ pub data: Vec<u64>, // least significant digit first, no trailing zeros
}
// Now that we fixed the data representation, we can start implementing methods on it.
impl BigInt {
pub fn new(x: u64) -> Self {
if x == 0 {
- BigInt { data: vec![] }
+ unimplemented!()
} else {
unimplemented!()
}
//
// **Exercise 05.1**: Implement this function.
//
- // *Hint*: You can use `pop()` to remove the last element of a vector.
+ // *Hint*: You can use `pop` to remove the last element of a vector.
pub fn from_vec(mut v: Vec<u64>) -> Self {
unimplemented!()
}
-// Rust-101, Part 09: Iterators (WIP)
-// ==================================
+// Rust-101, Part 09: Iterators
+// ============================
use part05::BigInt;
-// In the following, we will look into the iterator mechanism of Rust and make our `BigInt` compatible
-// with the `for` loops. Of course, this is all about implementing particular traits again. In particular,
-// an iterator is something that implements the `Iterator` trait. As you can see in [the documentation](http://doc.rust-lang.org/beta/std/iter/trait.Iterator.html),
-// this trait mandates a single function `next` returning an `Option<Self::Item>`, where `Item` is an
-// associated type chosen by the implementation. (There are many more methods provided for `Iterator`,
-// but they all have default implementations, so we don't have to worry about them right now).
-//
-// For the case of `BigInt`, we want our iterator to iterate over the digits in normal, notational order: The most-significant
-// digit comes first. So, we have to write down some type, and implement `Iterator` for it such that `next` returns the digits
-// one-by-one. Clearly, the iterator must somehow be able to access the number it iterates over, and it must store its current
-// location. However, it cannot *own* the `BigInt`, because then the number would be gone after iteration! That'd certainly be bad.
-// The only alternative is for the iterator to *borrow* the number.
-// In writing this down, we again have to be explicit about the lifetime of the borrow: We can't just have an
-// `Iter`, we must have an `Iter<'a>` that borrowed the number for lifetime `'a`. This is our first example of
-// a datatype that's polymorphic in a lifetime, as opposed to a type. <br/>
-// `usize` here is the type of unsigned, pointer-sized numbers. It is typically the type of "lengths of things",
-// in particular, it is the type of the length of a `Vec` and hence the right type to store an offset into the vector of digits.
-struct Iter<'a> {
+pub struct Iter<'a> {
num: &'a BigInt,
idx: usize, // the index of the last number that was returned
}
fn next(&mut self) -> Option<u64> {
// First, check whether there's any more digits to return.
if self.idx == 0 {
- // We already returned all the digits.
+ // We already returned all the digits, nothing to do.
unimplemented!()
} else {
- // Decrement, and return next digit.
+ // Otherwise: Decrement, and return next digit.
unimplemented!()
}
}
// All we need now is a function that creates such an iterator for a given `BigInt`.
impl BigInt {
- // Notice that when we write the type of `iter`, we don't actually have to give the lifetime parameter of `Iter`. Just as it is
- // the case with functions returning borrowed data, you can elide the lifetime. The rules for adding the lifetimes are exactly the
- // same. (See the last section of [part 06](part06.html).)
fn iter(&self) -> Iter {
unimplemented!()
}
// Of course, we don't have to use `for` to apply the iterator. We can also explicitly call `next`.
fn print_digits_v1(b: &BigInt) {
let mut iter = b.iter();
- // `loop` is the keyword for a loop without a condition: It runs endlessly, or until you break out of
- // it with `break` or `return`.
loop {
// Each time we go through the loop, we analyze the next element presented by the iterator - until it stops.
- match iter.next() {
- None => break,
- Some(digit) => println!("{}", digit)
- }
+ unimplemented!()
}
}
-// Now, it turns out that this combination of doing a loop and a pattern matching is fairly common, and Rust
-// provides some convenient syntactic sugar for it.
fn print_digits_v2(b: &BigInt) {
let mut iter = b.iter();
- // `while let` performs the given pattern matching on every round of the loop, and cancels the loop if the pattern
- // doesn't match. There's also `if let`, which works similar, but of course without the loopy part.
while let Some(digit) = iter.next() {
println!("{}", digit)
}
}
-// ## Iterator invalidation and lifetimes
-// You may have been surprised that we had to explicitly annotate a lifetime when we wrote `Iter`. Of
-// course, with lifetimes being present at every borrow in Rust, this is only consistent. But do we at
-// least gain something from this extra annotation burden? (Thankfully, this burden only occurs when we
-// define *types*, and not when we define functions - which is typically much more common.)
+// **Exercise 09.1**: Write a testcase for the iterator, making sure it yields the corrects numbers.
//
-// It turns out that the answer to this question is yes! This particular aspect of the concept of
-// lifetimes helps Rust to eliminate the issue of *iterator invalidation*. Consider the following
-// piece of code.
+// **Exercise 09.2**: Write a function `iter_ldf` that iterators over the digits with the least-significant
+// digits coming first. Write a testcase for it.
+
+// ## Iterator invalidation and lifetimes
+
fn iter_invalidation_demo() {
let mut b = BigInt::new(1 << 63) + BigInt::new(1 << 16) + BigInt::new(1 << 63);
for digit in b.iter() {
/*b = b + BigInt::new(1);*/ /* BAD! */
}
}
-// If you enable the bad line, Rust will reject the code. Why? The problem is that we are modifying the
-// number while iterating over it. In other languages, this can have all sorts of effects from inconsistent
-// data or throwing an exception (Java) to bad pointers being dereferenced (C++). Rust, however, is able to
-// detect this situation. When you call `iter`, you have to borrow `b` for some lifetime `'a`, and you obtain
-// `Iter<'a>`. This is an iterator that's only valid for lifetime `'a`. Gladly, we have this annotation available
-// to make such a statement. Now, since we are using the iterator throughout the loop, `'a` has to span the loop.
-// This `b` is borrowed for the duration of the loop, and we cannot mutate it. This is yet another example for
-// how the combination of mutation and aliasing leads to undesired effects (not necessarily crashes, like in Java),
-// which Rust successfully prevents.
-//
-// Technically speaking, there's one more subtlety that I did not explain yet. We never explicitly tied the lifetime `'a` of the
-// iterator to the loop so how does this happen? The answer lies in the full type of `next()`:
-// `fn<'a, 'b>(&'b mut Iter<'a>) -> Option<u64>`. Since `next()` takes a *borrowed* iterator, there are two lifetimes involved:
-// The lifetime of the borrow of the iterator, and the lifetime of the iterator itself. In such a case of nested lifetimes,
-// Rust implicitly adds the additional constraint that the inner lifetime *outlives* the outer one: The borrow of an iterator
-// cannot be valid for longer than the iterator itself is valid. This means that the lifetime `'a` of the iterator needs
-// to outlive every call to `next()`, and hence the loop. Lucky enough, this all happens without our intervention.
+// ## Iterator conversion trait
+
+impl<'a> IntoIterator for &'a BigInt {
+ type Item = u64;
+ type IntoIter = Iter<'a>;
+ fn into_iter(self) -> Iter<'a> {
+ self.iter()
+ }
+}
+// With this in place, you can now replace `b.iter()` in `main` by `&b`. Go ahead and try it! <br/>
projects / rust-101.git / commitdiff