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Diffstat (limited to 'security/sandbox/chromium/sandbox/linux/bpf_dsl/cons.h')
-rw-r--r-- | security/sandbox/chromium/sandbox/linux/bpf_dsl/cons.h | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/security/sandbox/chromium/sandbox/linux/bpf_dsl/cons.h b/security/sandbox/chromium/sandbox/linux/bpf_dsl/cons.h new file mode 100644 index 000000000..be050f778 --- /dev/null +++ b/security/sandbox/chromium/sandbox/linux/bpf_dsl/cons.h @@ -0,0 +1,139 @@ +// Copyright 2014 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef SANDBOX_LINUX_BPF_DSL_CONS_H_ +#define SANDBOX_LINUX_BPF_DSL_CONS_H_ + +#include "base/macros.h" +#include "base/memory/ref_counted.h" +#include "sandbox/sandbox_export.h" + +namespace sandbox { +namespace cons { + +// Namespace cons provides an abstraction for immutable "cons list" +// data structures as commonly provided in functional programming +// languages like Lisp or Haskell. +// +// A cons list is a linked list consisting of "cells", each of which +// have a "head" and a "tail" element. A cell's head element contains +// a user specified value, while the tail element contains a (possibly +// null) pointer to another cell. +// +// An empty list (idiomatically referred to as "nil") can be +// constructed as "cons::List<Foo>()" or simply as "nullptr" if Foo +// can be inferred from context (e.g., calling a function that has a +// "cons::List<Foo>" parameter). +// +// Existing lists (including empty lists) can be extended by +// prepending new values to the front using the "Cons(head, tail)" +// function, which will allocate a new cons cell. Notably, cons lists +// support creating multiple lists that share a common tail sequence. +// +// Lastly, lists support iteration via C++11's range-based for loop +// construct. +// +// Examples: +// +// // basic construction +// const cons::List<char> kNil = nullptr; +// cons::List<char> ba = Cons('b', Cons('a', kNil)); +// +// // common tail sequence +// cons::List<char> cba = Cons('c', ba); +// cons::List<char> dba = Cons('d', ba); +// +// // iteration +// for (const char& ch : cba) { +// // iterates 'c', 'b', 'a' +// } +// for (const char& ch : dba) { +// // iterates 'd', 'b', 'a' +// } + +// Forward declarations. +template <typename T> +class Cell; +template <typename T> +class ListIterator; + +// List represents a (possibly null) pointer to a cons cell. +template <typename T> +using List = scoped_refptr<const Cell<T>>; + +// Cons extends a cons list by prepending a new value to the front. +template <typename T> +List<T> Cons(const T& head, const List<T>& tail) { + return List<T>(new const Cell<T>(head, tail)); +} + +// Cell represents an individual "cons cell" within a cons list. +template <typename T> +class Cell : public base::RefCounted<Cell<T>> { + public: + Cell(const T& head, const List<T>& tail) : head_(head), tail_(tail) {} + + // Head returns this cell's head element. + const T& head() const { return head_; } + + // Tail returns this cell's tail element. + const List<T>& tail() const { return tail_; } + + private: + virtual ~Cell() {} + + T head_; + List<T> tail_; + + friend class base::RefCounted<Cell<T>>; + DISALLOW_COPY_AND_ASSIGN(Cell); +}; + +// Begin returns a list iterator pointing to the first element of the +// cons list. It's provided to support range-based for loops. +template <typename T> +ListIterator<T> begin(const List<T>& list) { + return ListIterator<T>(list); +} + +// End returns a list iterator pointing to the "past-the-end" element +// of the cons list (i.e., nil). It's provided to support range-based +// for loops. +template <typename T> +ListIterator<T> end(const List<T>& list) { + return ListIterator<T>(); +} + +// ListIterator provides C++ forward iterator semantics for traversing +// a cons list. +template <typename T> +class ListIterator { + public: + ListIterator() : list_() {} + explicit ListIterator(const List<T>& list) : list_(list) {} + + const T& operator*() const { return list_->head(); } + + ListIterator& operator++() { + list_ = list_->tail(); + return *this; + } + + friend bool operator==(const ListIterator& lhs, const ListIterator& rhs) { + return lhs.list_ == rhs.list_; + } + + private: + List<T> list_; +}; + +template <typename T> +bool operator!=(const ListIterator<T>& lhs, const ListIterator<T>& rhs) { + return !(lhs == rhs); +} + +} // namespace cons +} // namespace sandbox + +#endif // SANDBOX_LINUX_BPF_DSL_CONS_H_ |