traits.h File Reference

Compile-time type-trait utilities used internally by VLink. More...

#include <atomic>
#include <memory>
#include <type_traits>

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Classes
struct	vlink::Traits::EmptyType
	An empty tag type used as a neutral placeholder in template meta-programming. More...
struct	vlink::Traits::ExpectFalse< T >
	A type trait that always evaluates to std::false_type. More...
struct	vlink::Traits::Callable< T, typename >
	Detects whether type T is callable with no arguments. More...
struct	vlink::Traits::Callable< T, std::void_t< decltype(std::declval< T >()())> >
struct	vlink::Traits::Assignable< OT, T, typename >
	Detects whether an object of type OT can be assigned a value of type T. More...
struct	vlink::Traits::Assignable< OT, T, std::void_t< decltype(std::declval< OT & >()=std::declval< T >())> >
struct	vlink::Traits::EqualityComparable< OT, T, typename >
	Detects whether OT supports the == operator with T. More...
struct	vlink::Traits::EqualityComparable< OT, T, std::void_t< decltype(std::declval< OT >()==std::declval< T >())> >
struct	vlink::Traits::GreaterComparable< OT, T, typename >
	Detects whether OT supports both < and > operators with T. More...
struct	vlink::Traits::GreaterComparable< OT, T, std::void_t< decltype(std::declval< OT & >()< std::declval< T >()), decltype(std::declval< OT & >() > std::declval< T & >())> >
struct	vlink::Traits::Operatorable< OT, T, typename >
	Detects whether OT supports << and >> stream operators with T. More...
struct	vlink::Traits::Operatorable< OT, T, std::void_t< decltype(std::declval< OT & >()<< std::declval< T >()), decltype(std::declval< OT & >() > > std::declval< T & >())> >
struct	vlink::Traits::IsAtomic< T >
	Detects whether type T is a std::atomic specialization. More...
struct	vlink::Traits::IsAtomic< std::atomic< T > >
struct	vlink::Traits::IsSharedPtr< T, typename >
	Detects whether type T is a std::shared_ptr specialization. More...
struct	vlink::Traits::IsSharedPtr< T, std::void_t< typename T::element_type > >
struct	vlink::Traits::RemoveSharedPtr< T, bool >
	Strips std::shared_ptr to obtain the underlying element type. More...
struct	vlink::Traits::RemoveSharedPtr< T, true >

Namespaces
namespace	vlink
namespace	vlink::Traits
	Collection of compile-time type-trait helpers for VLink.

Macros
#define	VLINK_HAS_MEMBER(T, member)
	Macro Definitions.

Detailed Description

Compile-time type-trait utilities used internally by VLink.

The vlink::Traits namespace collects a set of small, self-contained template meta-programming helpers that are used throughout the VLink codebase to detect type properties at compile time. They follow the same conventions as the C++ standard library <type_traits> header.

All helpers are either:

• Struct templates inheriting from std::true_type / std::false_type, or
• constexpr functions returning bool.

Helper	Description
EmptyType	An empty tag type used as a placeholder
ExpectFalse	Always evaluates to std::false_type (useful in static_assert)
Callable	Detects whether T is callable with no arguments
Assignable	Detects whether OT is assignable from T
EqualityComparable	Detects whether OT supports == with T
GreaterComparable	Detects whether OT supports < and > with T
Operatorable	Detects whether OT supports << and >> stream operators with T
IsAtomic	Detects whether T is a std::atomic specialization
IsSharedPtr	Detects whether T is a std::shared_ptr specialization
RemoveSharedPtr	Strips the std::shared_ptr wrapper to obtain the element type
has_member	Runtime-style SFINAE check for a named member
is_non_char_ptr	True when T decays to a non-char pointer
is_integer	True for integer types excluding bool, char, and signed/unsigned char
is_floating	True for floating-point types

Note

These utilities live in the vlink::Traits namespace (note the capital T). VLINK_HAS_MEMBER is the corresponding macro wrapper for has_member.

Example: checking for a member at compile time

struct Foo { void bar() {} };
struct Baz {};
 
// Using the macro (preferred for member name checks):
static_assert(VLINK_HAS_MEMBER(Foo, bar));
static_assert(!VLINK_HAS_MEMBER(Baz, bar));
 
// Using the template directly:
static_assert(vlink::Traits::Callable<std::function<void()>>::value);

Macro Definition Documentation

VLINK_HAS_MEMBER

#define VLINK_HAS_MEMBER	(		T,
			member )

Value:

vlink::Traits::has_member<T>([](auto&& obj) -> decltype((void)(obj.member), 0) { return 0; })

Macro Definitions.

Checks at compile time whether type T has an accessible member named member.

Expands to a constexpr boolean expression (true/false) evaluated at compile time. Internally delegates to vlink::Traits::has_member.

Parameters

T	The type to inspect.
member	The unquoted member name to look for.

Example

struct Foo { int bar; };
static_assert(VLINK_HAS_MEMBER(Foo, bar));
static_assert(!VLINK_HAS_MEMBER(Foo, baz));