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Experimenting with string literals for non-type template parameters.
C++20 offers string literals as non-type template parameters and this would likely allow us to move away from using a clang extension which would allow for gcc support. This is just experimentation for now. See #4. Some previously stripped tags have been restored on targets in order to correctly filter C++20 targets. PiperOrigin-RevId: 687923300
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * Copyright 2024 Google LLC | ||
| * | ||
| * 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. | ||
| */ | ||
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| #ifndef JNI_BIND_METAPROGRAMMING_STRING_LITERAL_H_ | ||
| #define JNI_BIND_METAPROGRAMMING_STRING_LITERAL_H_ | ||
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| #ifdef __cplusplus | ||
| #if __cplusplus >= 202002L | ||
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| #include <algorithm> | ||
| #include <cstddef> | ||
| #include <string_view> | ||
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| namespace jni::metaprogramming { | ||
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| // Inspired by Kevin Hartman's StringLiteral implementation. | ||
| // https://ctrpeach.io/posts/cpp20-string-literal-template-parameters/ | ||
| // | ||
| // This class is not currently being used, but is being used to prototype | ||
| // changes that will be needed for consumers of `InvocableMap`. This class is | ||
| // not included by default for build because it requires C++20. | ||
| template <size_t N> | ||
| struct StringLiteral { | ||
| constexpr StringLiteral(const char (&str)[N]) { std::copy_n(str, N, value); } | ||
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| constexpr StringLiteral<N> Self() { return *this; } | ||
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| template <std::size_t U> | ||
| constexpr bool operator==(const StringLiteral<U>& rhs) const { | ||
| if constexpr (N != U) { | ||
| return false; | ||
| } else { | ||
| return std::string_view{value} == std::string_view{rhs.value}; | ||
| } | ||
| } | ||
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| template <std::size_t U> | ||
| constexpr bool operator!=(const StringLiteral<U>& rhs) const { | ||
| return !(*this == rhs); | ||
| } | ||
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| char value[N]; | ||
| }; | ||
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| template <size_t N> | ||
| StringLiteral(const char (&str)[N]) -> StringLiteral<N>; | ||
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| #endif // __cplusplus >= 202002L | ||
| #endif // __cplusplus | ||
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| } // namespace jni::metaprogramming | ||
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| #endif // JNI_BIND_METAPROGRAMMING_STRING_LITERAL_H_ |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| /* | ||
| * Copyright 2024 Google LLC | ||
| * | ||
| * 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. | ||
| */ | ||
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| #include "string_literal.h" | ||
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| #include <cstddef> | ||
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| using jni::metaprogramming::StringLiteral; | ||
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| namespace { | ||
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| template <size_t N> | ||
| constexpr StringLiteral<N> Foo(const char (&str)[N]) { | ||
| StringLiteral b{str}; | ||
| return b; | ||
| } | ||
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| // String literals can now peer through callsites. This was previously not | ||
| // possible in C++17 and should hopefully simplify method selection. | ||
| static_assert(Foo("Testing") == StringLiteral{"Testing"}); | ||
| static_assert(Foo("abcdefg") != StringLiteral{"Testing"}); | ||
| static_assert(Foo("Testing") != StringLiteral{"abcdefg"}); | ||
| static_assert(Foo("Bar") != StringLiteral{"Testing"}); | ||
| static_assert(Foo("Testing") != StringLiteral{"Bar"}); | ||
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| // This represents a container class. Any classes currently constructed with | ||
| // const char* will need to migrate to this new form which explicitly captures | ||
| // length. | ||
| template <std::size_t N> | ||
| struct SampleContainer { | ||
| constexpr SampleContainer(const char (&val_)[N]) : val_(val_) {} | ||
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| StringLiteral<N> val_; | ||
| }; | ||
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| template <std::size_t N> | ||
| SampleContainer(const char (&val_)[N]) -> SampleContainer<N>; | ||
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| static_assert(SampleContainer("Testing").val_ == StringLiteral{"Testing"}); | ||
| static_assert(SampleContainer("abcdefg").val_ != StringLiteral{"Testing"}); | ||
| static_assert(SampleContainer("Foo").val_ != StringLiteral{"Testing"}); | ||
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| } // namespace |