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add some comments for clarification

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This commit is contained in:
Oliver Schneider 2017-02-09 19:15:40 +01:00
parent c06251b0d2
commit 023ec3e395
1 changed files with 6 additions and 2 deletions
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8
src/terminator/drop.rs
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@ -79,10 +79,12 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
self.drop(Lvalue::Ptr { ptr, extra }, contents_ty, drop)?;
},
}
// We cannot use Box's destructor, because it is a no-op and only exists to reduce
// the number of hacks required in the compiler around the Box type.
let box_free_fn = self.tcx.lang_items.box_free_fn().expect("no box_free lang item");
let substs = self.tcx.intern_substs(&[Kind::from(contents_ty)]);
// this is somewhat hacky, but hey, there's no representation difference between
// pointers and references, so
// pointers, `Box`es and references, so
// #[lang = "box_free"] unsafe fn box_free<T>(ptr: *mut T)
// is the same as
// fn drop(&mut self) if Self is Box<T>
@ -164,7 +166,9 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
let drop_fn = self.memory.read_ptr(vtable)?;
// some values don't need to call a drop impl, so the value is null
if drop_fn != Pointer::from_int(0) {
let FunctionDefinition {def_id, substs, sig, ..} = self.memory.get_fn(drop_fn.alloc_id)?.expect_drop_glue()?;
// FIXME: change the `DropGlue` variant of `Function` to only contain `real_ty`
let FunctionDefinition {substs, sig, ..} = self.memory.get_fn(drop_fn.alloc_id)?.expect_drop_glue()?;
// The real type is taken from the self argument in `fn drop(&mut self)`
let real_ty = match sig.inputs()[0].sty {
ty::TyRef(_, mt) => self.monomorphize(mt.ty, substs),
_ => bug!("first argument of Drop::drop must be &mut T"),