1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70
/* * Copyright 2018 Google Inc. All rights reserved. * Copyright 2019 Butte authors. All rights reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ use crate::Error; use std::marker::PhantomData; /// Follow is a trait that allows us to access FlatBuffers in a declarative, /// type safe, and fast way. They compile down to almost no code (after /// optimizations). Conceptually, Follow lifts the offset-based access /// patterns of FlatBuffers data into the type system. This trait is used /// pervasively at read time, to access tables, vtables, vectors, strings, and /// all other data. At this time, Follow is not utilized much on the write /// path. /// /// Writing a new Follow implementation primarily involves deciding whether /// you want to return data (of the type Self::Inner) or do you want to /// continue traversing the FlatBuffer. pub trait Follow<'a> { type Inner; fn follow(buf: &'a [u8], loc: usize) -> Result<Self::Inner, Error>; } pub trait FollowBuf { type Buf: std::convert::AsRef<[u8]>; type Inner; fn follow_buf(buf: Self::Buf, loc: usize) -> Result<Self::Inner, Error>; } /// Execute a follow as a top-level function. #[allow(dead_code)] #[inline] pub fn lifted_follow<'a, T: Follow<'a>>(buf: &'a [u8], loc: usize) -> Result<T::Inner, Error> { T::follow(buf, loc) } /// FollowStart wraps a Follow impl in a struct type. This can make certain /// programming patterns more ergonomic. #[derive(Debug, Default)] pub struct FollowStart<T>(PhantomData<T>); impl<'a, T: Follow<'a> + 'a> FollowStart<T> { #[inline] pub fn new() -> Self { Self { 0: PhantomData } } #[inline] pub fn self_follow(&'a self, buf: &'a [u8], loc: usize) -> Result<T::Inner, Error> { T::follow(buf, loc) } } impl<'a, T: Follow<'a>> Follow<'a> for FollowStart<T> { type Inner = T::Inner; #[inline] fn follow(buf: &'a [u8], loc: usize) -> Result<Self::Inner, Error> { T::follow(buf, loc) } }