Squashed 'third_party/flatbuffers/' content from commit acc9990ab
Change-Id: I48550d40d78fea996ebe74e9723a5d1f910de491
git-subtree-dir: third_party/flatbuffers
git-subtree-split: acc9990abd2206491480291b0f85f925110102ea
diff --git a/rust/flatbuffers/src/follow.rs b/rust/flatbuffers/src/follow.rs
new file mode 100644
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+++ b/rust/flatbuffers/src/follow.rs
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+/*
+ * Copyright 2018 Google Inc. 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 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) -> Self::Inner;
+}
+
+/// 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) -> T::Inner {
+ T::follow(buf, loc)
+}
+
+/// FollowStart wraps a Follow impl in a struct type. This can make certain
+/// programming patterns more ergonomic.
+#[derive(Debug)]
+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) -> T::Inner {
+ 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) -> Self::Inner {
+ T::follow(buf, loc)
+ }
+}