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Clarify why 'static is free

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Who? Me?! 2018-10-22 12:37:13 -05:00
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6
src/doc/rustc-dev-guide/src/traits/canonicalization.md
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@ -42,7 +42,11 @@ This query contains two unbound variables, but it also contains the
lifetime `'static`. The trait system generally ignores all lifetimes
and treats them equally, so when canonicalizing, we will *also*
replace any [free lifetime](../appendix/background.html#free-vs-bound) with a
canonical variable. Therefore, we get the following result:
canonical variable (Note that `'static` is actually a _free_ lifetime
variable here. We are not considering it in the typing context of the whole
program but only in the context of this trait reference. Mathematically, we
are not quantifying over the whole program, but only this obligation).
Therefore, we get the following result:
```text
?0: Foo<'?1, ?2>