An ItemLocalId
uniquely identifies something within a given “item-like”;
that is, within a hir::Item
, hir::TraitItem
, or hir::ImplItem
. There is no
guarantee that the numerical value of a given ItemLocalId
corresponds to
the node’s position within the owning item in any way, but there is a
guarantee that the ItemLocalId
s within an owner occupy a dense range of
integers starting at zero, so a mapping that maps all or most nodes within
an “item-like” to something else can be implemented by a Vec
instead of a
tree or hash map.