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Document early exit of method candidate search #1394

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Document early exit of method candidate search #1394

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6 changes: 4 additions & 2 deletions src/expressions/method-call-expr.md
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Expand Up @@ -19,7 +19,7 @@ The following procedure is used:

The first step is to build a list of candidate receiver types.
Obtain these by repeatedly [dereferencing][dereference] the receiver expression's type, adding each type encountered to the list, then finally attempting an [unsized coercion] at the end, and adding the result type if that is successful.
Then, for each candidate `T`, add `&T` and `&mut T` to the list immediately after `T`.
Then, for each candidate `T`, add `&T` and `&mut T` to the ordered list immediately after `T`.

For instance, if the receiver has type `Box<[i32;2]>`, then the candidate types will be `Box<[i32;2]>`, `&Box<[i32;2]>`, `&mut Box<[i32;2]>`, `[i32; 2]` (by dereferencing), `&[i32; 2]`, `&mut [i32; 2]`, `[i32]` (by unsized coercion), `&[i32]`, and finally `&mut [i32]`.

Expand All @@ -30,6 +30,8 @@ Then, for each candidate type `T`, search for a [visible] method with a receiver
If `T` is a type parameter, methods provided by trait bounds on `T` are looked up first.
Then all remaining methods in scope are looked up.

As soon as one candidate type yielded a fitting method, the search process is stopped.

> Note: the lookup is done for each type in order, which can occasionally lead to surprising results.
> The below code will print "In trait impl!", because `&self` methods are looked up first, the trait method is found before the struct's `&mut self` method is found.
>
Expand Down Expand Up @@ -58,7 +60,7 @@ Then, for each candidate type `T`, search for a [visible] method with a receiver
> }
> ```

If this results in multiple possible candidates, then it is an error, and the receiver must be [converted][disambiguate call] to an appropriate receiver type to make the method call.
If any candidate type results in multiple possible methods, then it is an error, and the receiver must be [converted][disambiguate call] to an appropriate receiver type to make the method call.

This process does not take into account the mutability or lifetime of the receiver, or whether a method is `unsafe`.
Once a method is looked up, if it can't be called for one (or more) of those reasons, the result is a compiler error.
Expand Down