macros.h File Reference

Cross-platform macros for visibility, branch hints, copy prevention, singletons and string helpers. More...

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Macros
#define	VLINK_EXPORT   __attribute__((visibility("default")))
#define	VLINK_EXPORT_AND_ALIGNED(align_num)   VLINK_EXPORT __attribute__((aligned(align_num)))
	Marks a class or variable as both exported and aligned to align_num bytes. More...
#define	__has_builtin(x)   0
#define	VLINK_LIKELY(x)   (x)
#define	VLINK_UNLIKELY(x)   (x)
#define	VLINK_DISALLOW_COPY_AND_ASSIGN(classname)
	Deletes the copy constructor and copy-assignment operator of classname. More...
#define	VLINK_SINGLETON_CHECK(classname)
	Embeds a static check that enforces one-instance-per-process for classname. More...
#define	VLINK_SINGLETON_DECLARE(classname)
	Declares a Meyers singleton get and the matching uniqueness guards on classname. More...
#define	VLINK_MACRO_STRING_IFY(name)   #name
	Stringifies a token without performing macro expansion. More...
#define	VLINK_MACRO_STRING_GET(name)   VLINK_MACRO_STRING_IFY(name)
	Stringifies the expanded value of a macro (two-step expansion). More...
#define	VLINK_ASSERT_CONSTANT(msg)
#define	VLIKELY(...)   VLINK_LIKELY(__VA_ARGS__)
	Short alias for VLINK_LIKELY. More...
#define	VUNLIKELY(...)   VLINK_UNLIKELY(__VA_ARGS__)
	Short alias for VLINK_UNLIKELY. More...

Detailed Description

Cross-platform macros for visibility, branch hints, copy prevention, singletons and string helpers.

Every header in VLink relies on this file for ABI export decoration, alignment, branch prediction hints, and class-level boilerplate. Macros that depend on compiler features gracefully degrade to no-ops on platforms that do not expose those features.

Macro reference

Category	Macro	Purpose
Visibility	VLINK_EXPORT	DLL / shared-object visibility
Visibility + align	VLINK_EXPORT_AND_ALIGNED(n)	Combine export with byte alignment
Branch hints (long)	VLINK_LIKELY(x), VLINK_UNLIKELY(x)	C++20 [[likely]] / __builtin_expect
Branch hints (short)	VLIKELY(...), VUNLIKELY(...)	Aliases of VLINK_LIKELY / VLINK_UNLIKELY
Class hygiene	VLINK_DISALLOW_COPY_AND_ASSIGN(class)	Delete copy ctor and assignment
Singletons	VLINK_SINGLETON_CHECK(class)	Enforce one instance per process
Singletons	VLINK_SINGLETON_DECLARE(class)	Add get accessor + check + no-copy
Stringify	VLINK_MACRO_STRING_IFY(name)	Stringify a token directly
Stringify (eval)	VLINK_MACRO_STRING_GET(name)	Stringify after macro expansion
Constant check	VLINK_ASSERT_CONSTANT(msg)	static_assert message is a literal

Example

class VLINK_EXPORT MyService final {
  VLINK_DISALLOW_COPY_AND_ASSIGN(MyService)
 public:
  MyService();
};
 
if VLIKELY (ptr != nullptr) {
  ptr->do_something();
}

Note

VLINK_SINGLETON_CHECK enforces uniqueness at run time by tripping a std::atomic_flag the second time the constructor runs; the second instantiation throws std::runtime_error.

Macro Definition Documentation

__has_builtin

#define __has_builtin

(

x

)

0

VLIKELY

#define VLIKELY

(

...

)

VLINK_LIKELY(__VA_ARGS__)

Short alias for VLINK_LIKELY.

VLINK_ASSERT_CONSTANT

#define VLINK_ASSERT_CONSTANT

(

msg

)

VLINK_DISALLOW_COPY_AND_ASSIGN

#define VLINK_DISALLOW_COPY_AND_ASSIGN

(

classname

)

Value:

  classname(const classname&) = delete;           \
  classname& operator=(const classname&) = delete;

Deletes the copy constructor and copy-assignment operator of classname.

Drop the macro inside the private section of a class to prevent accidental copying.

Parameters

classname

Unqualified name of the enclosing class.

VLINK_EXPORT

#define VLINK_EXPORT   __attribute__((visibility("default")))

VLINK_EXPORT_AND_ALIGNED

#define VLINK_EXPORT_AND_ALIGNED

(

align_num

)

VLINK_EXPORT __attribute__((aligned(align_num)))

Marks a class or variable as both exported and aligned to align_num bytes.

Expands to __declspec(align(align_num)) on MSVC and to attribute((aligned(align_num))) on GCC / Clang.

Parameters

align_num

Required alignment in bytes; must be a power of two.

VLINK_LIKELY

#define VLINK_LIKELY

(

x

)

(x)

VLINK_MACRO_STRING_GET

#define VLINK_MACRO_STRING_GET

(

name

)

VLINK_MACRO_STRING_IFY(name)

Stringifies the expanded value of a macro (two-step expansion).

Use this form instead of VLINK_MACRO_STRING_IFY when name is itself a macro that should be expanded before stringification.

Parameters

name	Macro whose expansion is stringified.

VLINK_MACRO_STRING_IFY

#define VLINK_MACRO_STRING_IFY

(

name

)

#name

Stringifies a token without performing macro expansion.

Parameters

name	Token to stringify.

VLINK_SINGLETON_CHECK

#define VLINK_SINGLETON_CHECK

(

classname

)

Value:

 private:                                                                                         \
  struct ConstructorChecker {                                                                     \
    inline ConstructorChecker() {                                                                 \
      static_assert(std::is_final_v<classname>, "Constructor must be final.");                    \
      static_assert(!std::is_default_constructible_v<classname>, "Constructor must be private."); \
                                                                                                  \
      static std::atomic_flag flag;                                                               \
                                                                                                  \
      if VLINK_UNLIKELY (flag.test_and_set(std::memory_order_seq_cst)) {                          \
        throw std::runtime_error("Constructor has been instantiated.");                           \
      }                                                                                           \
    }                                                                                             \
  };                                                                                              \
                                                                                                  \
  ConstructorChecker constructor_checker_;

Embeds a static check that enforces one-instance-per-process for classname.

Combines two safeguards:

• Compile-time static_assert that classname is final and not externally default-constructible.
• Run-time std::atomic_flag trip that throws std::runtime_error on the second instantiation.

Parameters

classname

Unqualified name of the enclosing class.

Note

Place inside the private section of the class body.

VLINK_SINGLETON_DECLARE

#define VLINK_SINGLETON_DECLARE

(

classname

)

Value:

 public:                                      \
  inline static classname& get() {            \
    static classname singleton = classname(); \
    return singleton;                         \
  }                                           \
                                              \
 private:                                     \
  VLINK_SINGLETON_CHECK(classname)            \
  VLINK_DISALLOW_COPY_AND_ASSIGN(classname)

Declares a Meyers singleton get and the matching uniqueness guards on classname.

Expands to a public static get returning a reference to the single instance plus the VLINK_SINGLETON_CHECK and VLINK_DISALLOW_COPY_AND_ASSIGN macros.

Parameters

classname

Unqualified name of the singleton class.

Example

class MyService final {
  VLINK_SINGLETON_DECLARE(MyService)
 public:
  void do_work();
 private:
  MyService() = default;
};
 
MyService::get().do_work();

VLINK_UNLIKELY

#define VLINK_UNLIKELY

(

x

)

(x)

VUNLIKELY

#define VUNLIKELY

(

...

)

VLINK_UNLIKELY(__VA_ARGS__)

Short alias for VLINK_UNLIKELY.