Syntax highlight all rust code in librustc/traits/README.md
Also replace `...` with `/*...*/`
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@ -8,11 +8,15 @@ things.
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Trait resolution is the process of pairing up an impl with each
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reference to a trait. So, for example, if there is a generic function like:
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fn clone_slice<T:Clone>(x: &[T]) -> Vec<T> { ... }
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```rust
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fn clone_slice<T:Clone>(x: &[T]) -> Vec<T> { /*...*/ }
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```
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and then a call to that function:
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let v: Vec<isize> = clone_slice([1, 2, 3])
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```rust
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let v: Vec<isize> = clone_slice(&[1, 2, 3])
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```
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it is the job of trait resolution to figure out (in which case)
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whether there exists an impl of `isize : Clone`
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@ -21,12 +25,14 @@ Note that in some cases, like generic functions, we may not be able to
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find a specific impl, but we can figure out that the caller must
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provide an impl. To see what I mean, consider the body of `clone_slice`:
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fn clone_slice<T:Clone>(x: &[T]) -> Vec<T> {
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let mut v = Vec::new();
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for e in &x {
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v.push((*e).clone()); // (*)
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}
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```rust
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fn clone_slice<T:Clone>(x: &[T]) -> Vec<T> {
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let mut v = Vec::new();
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for e in &x {
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v.push((*e).clone()); // (*)
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}
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}
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```
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The line marked `(*)` is only legal if `T` (the type of `*e`)
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implements the `Clone` trait. Naturally, since we don't know what `T`
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@ -107,7 +113,7 @@ otherwise the result is considered ambiguous.
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This process is easier if we work through some examples. Consider
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the following trait:
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```
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```rust
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trait Convert<Target> {
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fn convert(&self) -> Target;
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}
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@ -119,8 +125,8 @@ wanted to permit conversion between `isize` and `usize`, we might
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implement `Convert` like so:
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```rust
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impl Convert<usize> for isize { ... } // isize -> usize
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impl Convert<isize> for usize { ... } // usize -> isize
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impl Convert<usize> for isize { /*...*/ } // isize -> usize
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impl Convert<isize> for usize { /*...*/ } // usize -> isize
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```
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Now imagine there is some code like the following:
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@ -205,12 +211,14 @@ using the definition of *matching* given above.
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Consider this simple example:
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trait A1 { ... }
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trait A2 : A1 { ... }
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```rust
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trait A1 { /*...*/ }
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trait A2 : A1 { /*...*/ }
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trait B { ... }
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trait B { /*...*/ }
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fn foo<X:A2+B> { ... }
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fn foo<X:A2+B> { /*...*/ }
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```
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Clearly we can use methods offered by `A1`, `A2`, or `B` within the
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body of `foo`. In each case, that will incur an obligation like `X :
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@ -247,10 +255,12 @@ to us, so we must run trait selection to figure everything out.
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Here is an example:
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trait Foo { ... }
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impl<U,T:Bar<U>> Foo for Vec<T> { ... }
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```rust
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trait Foo { /*...*/ }
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impl<U,T:Bar<U>> Foo for Vec<T> { /*...*/ }
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impl Bar<usize> for isize { ... }
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impl Bar<usize> for isize { /*...*/ }
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```
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After one shallow round of selection for an obligation like `Vec<isize>
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: Foo`, we would know which impl we want, and we would know that
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@ -343,7 +353,7 @@ Once the basic matching is done, we get to another interesting topic:
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how to deal with impl obligations. I'll work through a simple example
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here. Imagine we have the traits `Foo` and `Bar` and an associated impl:
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```
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```rust
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trait Foo<X> {
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fn foo(&self, x: X) { }
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}
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@ -401,7 +411,9 @@ Therefore, we search through impls and where clauses and so forth, and
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we come to the conclusion that the only possible impl is this one,
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with def-id 22:
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impl Foo<isize> for usize { ... } // Impl #22
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```rust
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impl Foo<isize> for usize { ... } // Impl #22
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```
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We would then record in the cache `usize : Foo<%0> ==>
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ImplCandidate(22)`. Next we would confirm `ImplCandidate(22)`, which
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