-// Rust-101, Part 06: Copy
-// =======================
+// Rust-101, Part 06: Copy, Lifetimes
+// ==================================
+// We continue to work on our `BigInt`, so we start by importing what we already established.
use part05::BigInt;
// With `BigInt` being about numbers, we should be able to write a version of `vec_min`
// that computes the minimum of a list of `BigInt`. We start by writing `min` for
// `BigInt`. Now our assumption of having no trailing zeros comes in handy!
impl BigInt {
- fn min(self, other: Self) -> Self {
- // Just to be sure, we first check that both operands actually satisfy our invariant.
- // `debug_assert!` is a macro that checks that its argument (must be of type `bool`)
- // is `true`, and panics otherwise. It gets removed in release builds, which you do with
- // `cargo build --release`.
+ fn min_try1(self, other: Self) -> Self {
+ // Just to be sure, we first check that both operands actually satisfy our invariant. `debug_assert!` is a
+ // macro that checks that its argument (must be of type `bool`) is `true`, and panics otherwise. It gets
+ // removed in release builds, which you do with `cargo build --release`.
debug_assert!(self.test_invariant() && other.test_invariant());
// If the lengths of the two numbers differ, we already know which is larger.
if self.data.len() < other.data.len() {
} else if self.data.len() > other.data.len() {
other
} else {
- // **Exercise 05.1**: Fill in this code.
- panic!("Not yet implemented.");
+ // **Exercise 06.1**: Fill in this code.
+ unimplemented!()
}
}
}
for e in v {
min = Some(match min {
None => e.clone(),
- Some(n) => e.clone().min(n)
+ Some(n) => e.clone().min_try1(n)
});
}
min
// 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
// 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 soon.
+// 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.
// ## `Copy` types
// But before we go there, I should answer the second question I brought up above: Why did our old `vec_min` work?
// stark contrast to types like `Vec<i32>`, where moving the value results in both the old and the new vector to
// point to the same underlying buffer. We don't have two vectors, there's no duplication.
//
-// Rust calls types that can be freely duplicated `Copy` types. `Copy` is another trait, and it
-// is implemented for types like `i32` and `bool`. Remember how we defined the trait `Minimum` by writing
-// `trait Minimum : Copy { ...`? This tells Rust that every type that implements `Minimum` must also
-// implement `Copy`, and that's why the compiler accepted our generic `vec_min` in part 02.
-// `Copy` is the first *marker trait* that we encounter: It does not provide any methods, but
-// makes a promise about the behavior of the type - in this case, being duplicable.
+// Rust calls types that can be freely duplicated `Copy` types. `Copy` is another trait, and it is implemented for
+// types like `i32` and `bool`. Remember how we defined the trait `Minimum` by writing `trait Minimum : Copy { ...`?
+// This tells Rust that every type that implements `Minimum` must also implement `Copy`, and that's why the compiler
+// accepted our generic `vec_min` in part 02. `Copy` is the first *marker trait* that we encounter: It does not provide
+// any methods, but makes a promise about the behavior of the type - in this case, being duplicable.
// If you try to implement `Copy` for `BigInt`, you will notice that Rust
// does not let you do that. A type can only be `Copy` if all its elements
// `Clone`. This makes the cost explicit.
// ## Lifetimes
-// To fix the performance problems of `vec_min`, we need ti 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*.
// This is demonstrated by the function `head` that borrows the first element of a vector if it is non-empty.
// Most of the time, we don't have to explicitly add lifetimes to function types. This is thanks to *lifetimes elision*,
// where Rust will automatically insert lifetimes we did not specify, following some [simple, well-documented rules](http://doc.rust-lang.org/stable/book/lifetimes.html#lifetime-elision).
-// [index](main.html) | [previous](part05.html) | [next](main.html)
+// [index](main.html) | [previous](part05.html) | [next](part07.html)
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