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borrowck/README.md: Clarify MUTABILITY and ALIASABLE

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Keegan McAllister 2015-02-18 18:07:03 -08:00
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src/librustc_borrowck/borrowck/README.md
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@ -261,12 +261,11 @@ that will go into the final loan. We'll discuss in more detail below.
## Checking mutability
Checking mutability is fairly straightforward. We just want to prevent
immutable data from being borrowed as mutable. Note that it is ok to
borrow mutable data as immutable, since that is simply a
freeze. Formally we define a predicate `MUTABLE(LV, MQ)` which, if
defined, means that "borrowing `LV` with mutability `MQ` is ok. The
Rust code corresponding to this predicate is the function
`check_mutability` in `middle::borrowck::gather_loans`.
immutable data from being borrowed as mutable. Note that it is ok to borrow
mutable data as immutable, since that is simply a freeze. The judgement
`MUTABILITY(LV, MQ)` means the mutability of `LV` is compatible with a borrow
of mutability `MQ`. The Rust code corresponding to this predicate is the
function `check_mutability` in `middle::borrowck::gather_loans`.
### Checking mutability of variables
@ -321,12 +320,11 @@ MUTABILITY(*LV, MQ) // M-Deref-Borrowed-Mut
## Checking aliasability
The goal of the aliasability check is to ensure that we never permit
`&mut` borrows of aliasable data. Formally we define a predicate
`ALIASABLE(LV, MQ)` which if defined means that
"borrowing `LV` with mutability `MQ` is ok". The
Rust code corresponding to this predicate is the function
`check_aliasability()` in `middle::borrowck::gather_loans`.
The goal of the aliasability check is to ensure that we never permit `&mut`
borrows of aliasable data. The judgement `ALIASABLE(LV, MQ)` means the
aliasability of `LV` is compatible with a borrow of mutability `MQ`. The Rust
code corresponding to this predicate is the function `check_aliasability()` in
`middle::borrowck::gather_loans`.
### Checking aliasability of variables