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auto merge of #14809 : zzmp/rust/patch-2, r=alexcrichton 

Previously, the type system's restrictions on borrowing were summarized as

> The previous example showed that the type system forbids any borrowing of owned boxes found in aliasable, mutable memory.

This did not jive with the example, which allowed mutations so long as the borrowed reference had been returned. Also, the language has changed to no longer allow aliasable mutable locations. This changes the summary to read

> The previous example showed that the type system forbids mutations of owned boxed values while they are being borrowed. In general, the type system also forbids borrowing a value as mutable if it is already being borrowed - either as a mutable reference or an immutable one.

This adds more general information for the experienced reader as well, to offer a more complete understanding.
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bors 2014-06-12 16:02:05 +00:00
parent c0a6f72e8b 4f90025b68
commit 8b87c3a2a8
1 changed files with 4 additions and 2 deletions
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src/doc/guide-lifetimes.md
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@ -275,8 +275,10 @@ invalidate the pointer `owner_age`.
# Borrowing and enums
The previous example showed that the type system forbids any borrowing
of owned boxes found in aliasable, mutable memory. This restriction
The previous example showed that the type system forbids any mutations
of owned boxed values while they are being borrowed. In general, the type
system also forbids borrowing a value as mutable if it is already being
borrowed - either as a mutable reference or an immutable one. This restriction
prevents pointers from pointing into freed memory. There is one other
case where the compiler must be very careful to ensure that pointers
remain valid: pointers into the interior of an `enum`.