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Example of constructing TuplePayload variants of enums.
PiperOrigin-RevId: 878549100
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‎docs/rust/enums.md‎

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### Example
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TODO(b/489757240): Add an example.
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Given the following Rust crate:
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```
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{{ #include ../../examples/rust/enum_with_payload/example.rs }}
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```
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<!-- class:Color -->
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Crubit will generate the following bindings:
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<!-- TODO(b/487357254): Add an example for StructPayloadVariant constructors
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once available. -->
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```
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{{ #include ../../examples/rust/enum_with_payload/example_generated.h }}
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```
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<!-- snippet:comment,block function:MakeRgb -->
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## Known issues
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‎examples/rust/enum_with_payload/BUILD‎

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load("@rules_cc//cc:cc_binary.bzl", "cc_binary")
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load(
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"@rules_rust//rust:defs.bzl",
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"rust_library",
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)
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load(
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"//cc_bindings_from_rs/bazel_support:cc_bindings_from_rust_rule.bzl",
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"cc_bindings_from_rust",
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)
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load(
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"//cc_bindings_from_rs/test/golden:golden_test.bzl",
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"golden_test",
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)
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package(default_applicable_licenses = ["//:license"])
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licenses(["notice"])
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rust_library(
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name = "example_crate",
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srcs = ["example.rs"],
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)
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cc_bindings_from_rust(
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name = "example_crate_cc_api",
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crate = ":example_crate",
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)
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cc_binary(
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name = "main",
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srcs = ["main.cc"],
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deps = [":example_crate_cc_api"],
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)
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golden_test(
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name = "example_golden_test",
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golden_h = "example_generated.h",
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rust_library = "example_crate",
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)

‎examples/rust/enum_with_payload/example.rs‎

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// Part of the Crubit project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#[derive(Copy, Clone)]
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pub enum Color {
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/// A completely transparent color (no payload)
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Transparent,
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/// A grayscale value from 0 to 255
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Grayscale(u8),
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/// Red, Green, and Blue values from 0 to 255
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Rgb(u8, u8, u8),
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}

‎examples/rust/enum_with_payload/example_generated.h‎

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// Part of the Crubit project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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// Automatically @generated C++ bindings for the following Rust crate:
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// example_crate_golden
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// Features: supported, types
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// clang-format off
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#ifndef THIRD_PARTY_CRUBIT_EXAMPLES_RUST_ENUM_WITH_PAYLOAD_EXAMPLE_CRATE_GOLDEN
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#define THIRD_PARTY_CRUBIT_EXAMPLES_RUST_ENUM_WITH_PAYLOAD_EXAMPLE_CRATE_GOLDEN
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#pragma clang diagnostic push
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#pragma clang diagnostic ignored "-Wreturn-type-c-linkage"
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#pragma clang diagnostic ignored "-Wunused-private-field"
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#pragma clang diagnostic ignored "-Wdeprecated-declarations"
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#include "support/annotations_internal.h"
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#include "support/internal/slot.h"
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#include <array>
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#include <cstddef>
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#include <cstdint>
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#include <cstring>
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#include <type_traits>
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#include <utility>
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namespace example_crate {
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// Generated from:
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// examples/rust/enum_with_payload/example.rs;l=6
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struct CRUBIT_INTERNAL_RUST_TYPE(":: example_crate_golden :: Color") alignas(1)
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[[clang::trivial_abi]] Color final {
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public:
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// `example_crate_golden::Color` doesn't implement the `Default` trait
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Color() = delete;
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// A completely transparent color (no payload)
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//
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// Generated from:
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// examples/rust/enum_with_payload/example.rs;l=8
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static constexpr Color MakeTransparent();
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// A grayscale value from 0 to 255
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//
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// Generated from:
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// examples/rust/enum_with_payload/example.rs;l=10
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static ::example_crate::Color MakeGrayscale(std::uint8_t __param_0);
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// Red, Green, and Blue values from 0 to 255
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//
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// Generated from:
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// examples/rust/enum_with_payload/example.rs;l=12
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static ::example_crate::Color MakeRgb(std::uint8_t __param_0,
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std::uint8_t __param_1,
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std::uint8_t __param_2);
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// No custom `Drop` impl and no custom "drop glue" required
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~Color() = default;
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Color(Color&&) = default;
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::example_crate::Color& operator=(Color&&) = default;
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// Rust types that are `Copy` get trivial, `default` C++ copy constructor and
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// assignment operator.
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Color(const Color&) = default;
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::example_crate::Color& operator=(const Color&) = default;
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Color(::crubit::UnsafeRelocateTag, Color&& value) {
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std::memcpy(this, &value, sizeof(value));
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}
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private:
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// Field type has been replaced with a blob of bytes: No support for bindings
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// of individual non-repr(C) `enum`s
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std::array<unsigned char, 4> __opaque_blob_of_bytes;
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private:
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struct PrivateBytesTag {};
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constexpr Color(PrivateBytesTag, std::array<unsigned char, 4> bytes)
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: __opaque_blob_of_bytes(bytes) {}
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private:
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static void __crubit_field_offset_assertions();
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};
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static_assert(
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sizeof(Color) == 4,
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"Verify that ADT layout didn't change since this header got generated");
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static_assert(
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alignof(Color) == 1,
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"Verify that ADT layout didn't change since this header got generated");
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// `static` constructor
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inline constexpr Color Color::MakeTransparent() {
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return Color(PrivateBytesTag{}, {0, 0, 0, 0});
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}
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namespace __crubit_internal {
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extern "C" void __crubit_thunk_Grayscale(std::uint8_t,
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::example_crate::Color* __ret_ptr);
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}
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inline ::example_crate::Color Color::MakeGrayscale(std::uint8_t __param_0) {
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crubit::Slot<::example_crate::Color> __return_value_ret_val_holder;
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auto* __return_value_storage = __return_value_ret_val_holder.Get();
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__crubit_internal::__crubit_thunk_Grayscale(__param_0,
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__return_value_storage);
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return std::move(__return_value_ret_val_holder).AssumeInitAndTakeValue();
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}
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namespace __crubit_internal {
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extern "C" void __crubit_thunk_Rgb(std::uint8_t, std::uint8_t, std::uint8_t,
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::example_crate::Color* __ret_ptr);
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}
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inline ::example_crate::Color Color::MakeRgb(std::uint8_t __param_0,
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std::uint8_t __param_1,
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std::uint8_t __param_2) {
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crubit::Slot<::example_crate::Color> __return_value_ret_val_holder;
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auto* __return_value_storage = __return_value_ret_val_holder.Get();
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__crubit_internal::__crubit_thunk_Rgb(__param_0, __param_1, __param_2,
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__return_value_storage);
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return std::move(__return_value_ret_val_holder).AssumeInitAndTakeValue();
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}
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static_assert(std::is_trivially_destructible_v<Color>);
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static_assert(std::is_trivially_move_constructible_v<::example_crate::Color>);
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static_assert(std::is_trivially_move_assignable_v<::example_crate::Color>);
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static_assert(std::is_trivially_copy_constructible_v<::example_crate::Color>);
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static_assert(std::is_trivially_copy_assignable_v<::example_crate::Color>);
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inline void Color::__crubit_field_offset_assertions() {
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static_assert(0 == offsetof(Color, __opaque_blob_of_bytes));
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}
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} // namespace example_crate
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#pragma clang diagnostic pop
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#endif // THIRD_PARTY_CRUBIT_EXAMPLES_RUST_ENUM_WITH_PAYLOAD_EXAMPLE_CRATE_GOLDEN

‎examples/rust/enum_with_payload/main.cc‎

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// Part of the Crubit project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#include <utility>
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#include "examples/rust/enum_with_payload/example_crate.h"
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int main(int argc, char* argv[]) {
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example_crate::Color transparent_color =
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example_crate::Color::MakeTransparent();
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example_crate::Color red_color = example_crate::Color::MakeRgb(255, 0, 0);
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std::ignore = transparent_color;
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std::ignore = red_color;
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return 0;
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}

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