1 /*
2 * Copyright 2018 Google Inc. All rights reserved.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 use std::marker::PhantomData;
18
19 /// Follow is a trait that allows us to access FlatBuffers in a declarative,
20 /// type safe, and fast way. They compile down to almost no code (after
21 /// optimizations). Conceptually, Follow lifts the offset-based access
22 /// patterns of FlatBuffers data into the type system. This trait is used
23 /// pervasively at read time, to access tables, vtables, vectors, strings, and
24 /// all other data. At this time, Follow is not utilized much on the write
25 /// path.
26 ///
27 /// Writing a new Follow implementation primarily involves deciding whether
28 /// you want to return data (of the type Self::Inner) or do you want to
29 /// continue traversing the FlatBuffer.
30 pub trait Follow<'a> {
31 type Inner;
follow(buf: &'a [u8], loc: usize) -> Self::Inner32 fn follow(buf: &'a [u8], loc: usize) -> Self::Inner;
33 }
34
35 /// Execute a follow as a top-level function.
36 #[allow(dead_code)]
37 #[inline]
lifted_follow<'a, T: Follow<'a>>(buf: &'a [u8], loc: usize) -> T::Inner38 pub fn lifted_follow<'a, T: Follow<'a>>(buf: &'a [u8], loc: usize) -> T::Inner {
39 T::follow(buf, loc)
40 }
41
42 /// FollowStart wraps a Follow impl in a struct type. This can make certain
43 /// programming patterns more ergonomic.
44 #[derive(Debug)]
45 pub struct FollowStart<T>(PhantomData<T>);
46 impl<'a, T: Follow<'a> + 'a> FollowStart<T> {
47 #[inline]
new() -> Self48 pub fn new() -> Self {
49 Self { 0: PhantomData }
50 }
51 #[inline]
self_follow(&'a self, buf: &'a [u8], loc: usize) -> T::Inner52 pub fn self_follow(&'a self, buf: &'a [u8], loc: usize) -> T::Inner {
53 T::follow(buf, loc)
54 }
55 }
56 impl<'a, T: Follow<'a>> Follow<'a> for FollowStart<T> {
57 type Inner = T::Inner;
58 #[inline]
follow(buf: &'a [u8], loc: usize) -> Self::Inner59 fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
60 T::follow(buf, loc)
61 }
62 }
63