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46 lines
1.7 KiB
46 lines
1.7 KiB
4 months ago
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// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef MOJO_PUBLIC_CPP_BINDINGS_UNION_TRAITS_H_
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#define MOJO_PUBLIC_CPP_BINDINGS_UNION_TRAITS_H_
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#include "mojo/public/cpp/bindings/lib/template_util.h"
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namespace mojo {
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// This must be specialized for any type |T| to be serialized/deserialized as
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// a mojom union. |DataViewType| is the corresponding data view type of the
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// mojom union. For example, if the mojom union is example.Foo, |DataViewType|
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// will be example::FooDataView, which can also be referred to by
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// example::Foo::DataView (in chromium) and example::blink::Foo::DataView (in
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// blink).
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//
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// Similar to StructTraits, each specialization of UnionTraits implements the
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// following methods:
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// 1. Getters for each field in the Mojom type.
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// 2. Read() method.
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// 3. [Optional] IsNull() and SetToNull().
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// 4. [Optional] SetUpContext() and TearDownContext().
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// Please see the documentation of StructTraits for details of these methods.
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//
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// Unlike StructTraits, there is one more method to implement:
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// 5. A static GetTag() method indicating which field is the current active
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// field for serialization:
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//
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// static DataViewType::Tag GetTag(const T& input);
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//
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// During serialization, only the field getter corresponding to this tag
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// will be called.
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//
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template <typename DataViewType, typename T>
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struct UnionTraits {
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static_assert(internal::AlwaysFalse<T>::value,
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"Cannot find the mojo::UnionTraits specialization. Did you "
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"forget to include the corresponding header file?");
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};
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} // namespace mojo
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#endif // MOJO_PUBLIC_CPP_BINDINGS_UNION_TRAITS_H_
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