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[canonicalization] fix result canonicalization example #304

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May 4, 2019
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[canonicalization] fix result canonicalization example #304

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2 changes: 1 addition & 1 deletion src/traits/canonical-queries.md
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Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,7 @@ variables have unbound inference variables in their type: `?T`
represents the elements in the vector `t` and `?U` represents the
value stored in the option `u`. Next, we invoke `foo`; comparing the
signature of `foo` to its arguments, we wind up with `A = Vec<?T>` and
`B = ?U`.Therefore, the where clause on `foo` requires that `Vec<?T>:
`B = ?U`. Therefore, the where clause on `foo` requires that `Vec<?T>:
Borrow<?U>`. This is thus our first example trait query.

There are many possible solutions to the query `Vec<?T>: Borrow<?U>`;
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10 changes: 5 additions & 5 deletions src/traits/canonicalization.md
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Expand Up @@ -177,8 +177,8 @@ The result would be as follows:
```text
Canonical(QR) = for<T, L> {
certainty: Proven,
var_values: [Vec<?0>, '?1, ?2]
region_constraints: [?2: '?1],
var_values: [Vec<?0>, '?1, ?0]
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This is the change I am not exactly sure about and would like to get reviewed.

From all that I understand, this ?2 ought to be ?0 (because we canonicalizing the same variable ?E).
for<T, L> also suggests that there should be only two canonical variables.

cc original author @nikomatsakis

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Yes, that sounds right, but I will defer to an expert like @nikomatsakis @tmandry or @scalexm ...

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Ping @scalexm?

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This is correct

region_constraints: [?0: '?1],
value: (),
}
```
Expand Down Expand Up @@ -213,8 +213,8 @@ and now we got back a canonical response:
```text
for<T, L> {
certainty: Proven,
var_values: [Vec<?0>, '?1, ?2]
region_constraints: [?2: '?1],
var_values: [Vec<?0>, '?1, ?0]
region_constraints: [?0: '?1],
value: (),
}
```
Expand Down Expand Up @@ -250,7 +250,7 @@ for later verification.
than eagerly instantiating all of the canonical values in the result
with variables, we instead walk the vector of values, looking for
cases where the value is just a canonical variable. In our example,
`values[2]` is `?C`, so that means we can deduce that `?C := ?B and
`values[2]` is `?C`, so that means we can deduce that `?C := ?B` and
`'?D := 'static`. This gives us a partial set of values. Anything for
which we do not find a value, we create an inference variable.)