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Add more explanation for why the assumes are there

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This commit is contained in:
James Miller 2015-01-21 09:56:59 +13:00
parent 9bbfd681c9
commit a7525bc4c8
1 changed files with 9 additions and 1 deletions
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10
src/liballoc/rc.rs
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@ -909,6 +909,8 @@ trait RcBoxPtr<T> {
fn inc_strong(&self) {
let strong = self.strong();
// The reference count is always at least one unless we're about to drop the type
// This allows the bulk of the destructor to be omitted in cases where we know that
// the reference count must be > 0.
unsafe { assume(strong > 0); }
self.inner().strong.set(strong + 1);
}
@ -917,6 +919,8 @@ trait RcBoxPtr<T> {
fn dec_strong(&self) {
let strong = self.strong();
// The reference count is always at least one unless we're about to drop the type
// This allows the bulk of the destructor to be omitted in cases where we know that
// the reference count must be > 0
unsafe { assume(strong > 0); }
self.inner().strong.set(strong - 1);
}
@ -936,7 +940,9 @@ impl<T> RcBoxPtr<T> for Rc<T> {
fn inner(&self) -> &RcBox<T> {
unsafe {
// Safe to assume this here, as if it weren't true, we'd be breaking
// the contract anyway
// the contract anyway.
// This allows the null check to be elided in the destructor if we
// manipulated the reference count in the same function.
assume(!self._ptr.is_null());
&(**self._ptr)
}
@ -949,6 +955,8 @@ impl<T> RcBoxPtr<T> for Weak<T> {
unsafe {
// Safe to assume this here, as if it weren't true, we'd be breaking
// the contract anyway
// This allows the null check to be elided in the destructor if we
// manipulated the reference count in the same function.
assume(!self._ptr.is_null());
&(**self._ptr)
}