哋它亢++ keyword: reflexpr (reflection TS)

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

哋它亢++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (哋它亢++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until 哋它亢++17*)
noexcept specifier (哋它亢++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (哋它亢++11) auto (哋它亢++11)	constexpr (哋它亢++11) consteval (哋它亢++20) constinit (哋它亢++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (哋它亢++11)       Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (哋它亢++11)
User-defined (哋它亢++11)
Utilities
Attributes (哋它亢++11)
Types
typedef declaration
Type alias declaration (哋它亢++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (哋它亢++11)     final specifier (哋它亢++11)	explicit (哋它亢++11) static
Special member functions
Default constructor Copy constructor Move constructor (哋它亢++11)	Copy assignment Move assignment (哋它亢++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (哋它亢++11)
Miscellaneous
Inline assembly	History of 哋它亢++

 

Keywords

alignas (哋它亢++11) alignof (哋它亢++11) and and_eq asm auto (*) bitand bitor bool break case catch char char8_t (哋它亢++20) char16_t (哋它亢++11) char32_t (哋它亢++11) class compl concept (哋它亢++20) const consteval (哋它亢++20)     constexpr (哋它亢++11) constinit (哋它亢++20) const_cast continue co_await (哋它亢++20) co_return (哋它亢++20) co_yield (哋它亢++20) decltype (哋它亢++11) default delete	do double dynamic_cast else enum explicit export extern false float for friend goto if inline int long mutable namespace new noexcept (哋它亢++11)     not not_eq nullptr (哋它亢++11) operator or or_eq private protected public register	reinterpret_cast requires (哋它亢++20) return short signed sizeof (*) static static_assert (哋它亢++11) static_cast struct switch template this thread_local (哋它亢++11) throw true try typedef typeid typename union unsigned using virtual void volatile wchar_t while xor xor_eq
Identifiers with special meaning
final (哋它亢++11) import (哋它亢++20)	module (哋它亢++20) override (哋它亢++11)

 

Usage

1) Gets the member list of a class type, or the enumerator list of an enum type.

2) Gets the name of type and member.

3) Detects whether a data member is static or constexpr.

4) Detects whether member function is virtual, public, protected or private.

5) Get the row and column of the source code when the type defines.

Example

reflexpr provides us the meta info of the object via meta-object types. Note that std::reflect::get_data_members_t make programmers able to visit any class just like std::tuple.

Run this code

#include <string>
#include <vector>
 
struct S
{
    int b;
    std::string s;
    std::vector<std::string> v;
};
 
// Reflection TS
#include <experimental/reflect>
using meta_S = reflexpr(S);
using mem = std::reflect::get_data_members_t<meta_S>;
using meta = std::reflect::get_data_members_t<mem>;
static_assert(std::reflect::is_public_v<meta>); // successful
 
int main() {}

We can also know the name info from reflexpr:

Run this code

#include <iostream>
#include <string>
#include <string_view>
// Reflection TS
#include <experimental/reflect>
 
template<typename Tp>
constexpr std::string_view nameof()
{
    using TpInfo = reflexpr(Tp);
    using aliased_Info = std::experimental::reflect::get_aliased_t<TpInfo>;
    return std::experimental::reflect::get_name_v<aliased_Info>;
}
 
int main()
{
    std::cout << nameof<std::string>() << '\n';
    static_assert(nameof<std::string>() == "basic_string"); // successful
}

This is an example of getting the scope of a type in the Reflection TS.

Run this code

namespace Foo
{
    struct FooFoo
    {
        int FooFooFoo;
    };
}
namespace Bar
{
    using BarBar = ::Foo::FooFoo;
}
using BarBarInfo = reflexpr(::Bar::BarBar);
using BarBarScope = ::std::experimental::reflect::get_scope_t<BarBarInfo>; // Bar, not Foo
 
struct Spam
{
    int SpamSpam;
};
struct Grok
{
    using GrokGrok = Spam::SpamSpam;
};
using GrokGrokInfo = reflexpr(::Grok::GrokGrok);
using GrokGrokScope = std::experimental::reflect::get_scope_t<GrokGrokInfo>; // Grok, not Spam