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[C++17] Add Traits class for Tables and Factory function within it. (#5678)

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* Include flattests_cpp17 in unit tests when C++17 build is enabled.

* [C++17] Generate generic table factory function.

1. For each table, generate a convenient free-standing factory
   function that allows creating the table in a generic way by
   specifying only the type.  This is the first change in a series
   of changes to make Flatbuffers generated C++ code more friendly
   to code bases that make use of C++ template metaprogramming
   techniques to manage the serialization process.  Example:

     Before :(

       // The name of the Flatbuffers type (and namespace) must
       // be hard-coded when writing the factory function.
       auto monster = MyGame::Example::CreateMonster(fbb, ...);

     After  :)

       using type_to_create = MyGame::Example::Monster;
       // No namespace needed on CreateByTagType.
       auto monster = CreateByTagType((type_to_create*)nullptr,
                                      fbb, ...);

   This feature requires building with C++14 or greater, and thus
   it is guarded behind --cpp-std >= c++17 in the flatbuffers C++
   generator.

2. Fix a CMake bug to include C++17 unit tests in test suite.

* [C++17] Replace standalone variadic factory function with type_traits.

Add a `type_traits` to each table class.  This `type_traits` can be
populated with various compile-time info about the table.  Initially,
we have the Create* function and type, but is extensible in the future.

* Remove empty line and fix stale comments.

* Rename type_traits to Traits and move fwd declaration.

* Fix parameter evaluation order issue and use lambda for scope.
This commit is contained in:
David P. Sicilia
2020-01-02 13:12:14 -05:00
committed by Wouter van Oortmerssen
parent 3cd9b6434a
commit a5d9d0f7d3
4 changed files with 82 additions and 1 deletions
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42
tests/cpp17/generated_cpp17/monster_test_generated.h
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@@ -621,6 +621,7 @@ struct InParentNamespaceT : public flatbuffers::NativeTable {
struct InParentNamespace FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef InParentNamespaceT NativeTableType;
typedef InParentNamespaceBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return InParentNamespaceTypeTable();
}
@@ -655,6 +656,11 @@ inline flatbuffers::Offset<InParentNamespace> CreateInParentNamespace(
return builder_.Finish();
}
struct InParentNamespace::Traits {
using type = InParentNamespace;
static auto constexpr Create = CreateInParentNamespace;
};
flatbuffers::Offset<InParentNamespace> CreateInParentNamespace(flatbuffers::FlatBufferBuilder &_fbb, const InParentNamespaceT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
namespace Example2 {
@@ -668,6 +674,7 @@ struct MonsterT : public flatbuffers::NativeTable {
struct Monster FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef MonsterT NativeTableType;
typedef MonsterBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return MonsterTypeTable();
}
@@ -702,6 +709,11 @@ inline flatbuffers::Offset<Monster> CreateMonster(
return builder_.Finish();
}
struct Monster::Traits {
using type = Monster;
static auto constexpr Create = CreateMonster;
};
flatbuffers::Offset<Monster> CreateMonster(flatbuffers::FlatBufferBuilder &_fbb, const MonsterT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
} // namespace Example2
@@ -719,6 +731,7 @@ struct TestSimpleTableWithEnumT : public flatbuffers::NativeTable {
struct TestSimpleTableWithEnum FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef TestSimpleTableWithEnumT NativeTableType;
typedef TestSimpleTableWithEnumBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return TestSimpleTableWithEnumTypeTable();
}
@@ -768,6 +781,11 @@ inline flatbuffers::Offset<TestSimpleTableWithEnum> CreateTestSimpleTableWithEnu
return builder_.Finish();
}
struct TestSimpleTableWithEnum::Traits {
using type = TestSimpleTableWithEnum;
static auto constexpr Create = CreateTestSimpleTableWithEnum;
};
flatbuffers::Offset<TestSimpleTableWithEnum> CreateTestSimpleTableWithEnum(flatbuffers::FlatBufferBuilder &_fbb, const TestSimpleTableWithEnumT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
struct StatT : public flatbuffers::NativeTable {
@@ -784,6 +802,7 @@ struct StatT : public flatbuffers::NativeTable {
struct Stat FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef StatT NativeTableType;
typedef StatBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return StatTypeTable();
}
@@ -860,6 +879,11 @@ inline flatbuffers::Offset<Stat> CreateStat(
return builder_.Finish();
}
struct Stat::Traits {
using type = Stat;
static auto constexpr Create = CreateStat;
};
inline flatbuffers::Offset<Stat> CreateStatDirect(
flatbuffers::FlatBufferBuilder &_fbb,
const char *id = nullptr,
@@ -886,6 +910,7 @@ struct ReferrableT : public flatbuffers::NativeTable {
struct Referrable FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef ReferrableT NativeTableType;
typedef ReferrableBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return ReferrableTypeTable();
}
@@ -941,6 +966,11 @@ inline flatbuffers::Offset<Referrable> CreateReferrable(
return builder_.Finish();
}
struct Referrable::Traits {
using type = Referrable;
static auto constexpr Create = CreateReferrable;
};
flatbuffers::Offset<Referrable> CreateReferrable(flatbuffers::FlatBufferBuilder &_fbb, const ReferrableT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
struct MonsterT : public flatbuffers::NativeTable {
@@ -1017,6 +1047,7 @@ struct MonsterT : public flatbuffers::NativeTable {
struct Monster FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef MonsterT NativeTableType;
typedef MonsterBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return MonsterTypeTable();
}
@@ -1766,6 +1797,11 @@ inline flatbuffers::Offset<Monster> CreateMonster(
return builder_.Finish();
}
struct Monster::Traits {
using type = Monster;
static auto constexpr Create = CreateMonster;
};
inline flatbuffers::Offset<Monster> CreateMonsterDirect(
flatbuffers::FlatBufferBuilder &_fbb,
const MyGame::Example::Vec3 *pos = 0,
@@ -1920,6 +1956,7 @@ struct TypeAliasesT : public flatbuffers::NativeTable {
struct TypeAliases FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
typedef TypeAliasesT NativeTableType;
typedef TypeAliasesBuilder Builder;
struct Traits;
static const flatbuffers::TypeTable *MiniReflectTypeTable() {
return TypeAliasesTypeTable();
}
@@ -2114,6 +2151,11 @@ inline flatbuffers::Offset<TypeAliases> CreateTypeAliases(
return builder_.Finish();
}
struct TypeAliases::Traits {
using type = TypeAliases;
static auto constexpr Create = CreateTypeAliases;
};
inline flatbuffers::Offset<TypeAliases> CreateTypeAliasesDirect(
flatbuffers::FlatBufferBuilder &_fbb,
int8_t i8 = 0,