flatbuffers/
follow.rs

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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
17use core::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.
30pub trait Follow<'buf> {
31    type Inner;
32    /// # Safety
33    ///
34    /// `buf[loc..]` must contain a valid value of `Self` and anything it
35    /// transitively refers to by offset must also be valid
36    unsafe fn follow(buf: &'buf [u8], loc: usize) -> Self::Inner;
37}
38
39/// FollowStart wraps a Follow impl in a struct type. This can make certain
40/// programming patterns more ergonomic.
41#[derive(Debug, Default)]
42pub struct FollowStart<T>(PhantomData<T>);
43impl<'a, T: Follow<'a> + 'a> FollowStart<T> {
44    #[inline]
45    pub fn new() -> Self {
46        Self(PhantomData)
47    }
48
49    /// # Safety
50    ///
51    /// `buf[loc..]` must contain a valid value of `T`
52    #[inline]
53    pub unsafe fn self_follow(&'a self, buf: &'a [u8], loc: usize) -> T::Inner {
54        T::follow(buf, loc)
55    }
56}
57impl<'a, T: Follow<'a>> Follow<'a> for FollowStart<T> {
58    type Inner = T::Inner;
59    #[inline]
60    unsafe fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
61        T::follow(buf, loc)
62    }
63}
flatbuffers/follow.rs

flatbuffers/
follow.rs
