Miscellaneous Utilities

Other small helper utilities. More...

Collaboration diagram for Miscellaneous Utilities:

Files
file	uuid.h
	Universally Unique Identifier (UUID) support.

Classes
struct	qb::nocopy
	Base class to make derived classes non-copyable. More...

Functions
bool	qb::likely (bool expr)
	Hint for branch prediction when a condition is expected to be true.
bool	qb::unlikely (bool expr)
	Hint for branch prediction when a condition is expected to be false.
template<typename... Types>
size_t	qb::hash_combine (const Types &...args)
	Combines the hash values of multiple objects into a single hash value.
template<typename T>
std::remove_reference_t< T > &&	mv (T &&t) noexcept
	Alias for std::move with a concise syntax.
template<typename T>
T &&	fwd (std::remove_reference_t< T > &t) noexcept
	Alias for std::forward with a concise syntax (lvalue overload).
template<typename T>
T &&	fwd (std::remove_reference_t< T > &&t) noexcept
	Alias for std::forward with a concise syntax (rvalue overload).

Detailed Description

Other small helper utilities.

Includes `qb::nocopy`, `qb::functional`, branch prediction hints, etc.

Function Documentation

likely()

bool qb::likely ( bool expr )

inline

Hint for branch prediction when a condition is expected to be true.

Parameters

expr	Boolean expression to evaluate.

Returns

The result of evaluating expr.

Use this function to indicate to the compiler that the expression expr is expected to evaluate to true most of the time. This can help the compiler optimize code paths that are frequently taken, potentially improving performance by reducing branch mispredictions. Typically implemented using __builtin_expect on GCC/Clang.

if (qb::likely(common_case_condition)) {
  // Optimized path for likely true
} else {
  // Path for less common false case
}

unlikely()

bool qb::unlikely ( bool expr )

inline

Hint for branch prediction when a condition is expected to be false.

Parameters

expr	Boolean expression to evaluate.

Returns

The result of evaluating expr.

Use this function to indicate to the compiler that the expression expr is expected to evaluate to false most of the time. This can help the compiler optimize for the more common case where the branch is not taken, or the alternative path is taken. Typically implemented using __builtin_expect on GCC/Clang.

if (qb::unlikely(error_condition)) {
  // Path for rare error case
} else {
  // Optimized path for likely non-error
}

hash_combine()

template<typename... Types>

size_t qb::hash_combine

(

const Types &...

args

)

Combines the hash values of multiple objects into a single hash value.

Template Parameters

Types

Variadic template parameter pack of the types of objects to hash.

Parameters

args	The values whose hash codes are to be combined.

Returns

A single size_t hash value representing the combination of all input values.

This function is particularly useful for creating custom hash functions for composite objects (structs or classes) to be used as keys in hash-based containers like qb::unordered_map or std::unordered_map. It iteratively combines the hash of each argument into a seed.

struct MyKey {
    int id;
    std::string name;
    double value;
 
    bool operator==(const MyKey& other) const {
        return id == other.id && name == other.name && value == other.value;
    }
};
 
namespace std {
  template <>
  struct hash<MyKey> {
    std::size_t operator()(const MyKey& k) const {
      return qb::hash_combine(k.id, k.name, k.value);
    }
  };
} // namespace std
 
// ... later ...
// qb::unordered_map<MyKey, SomeData> my_map;

mv()

template<typename T>

std::remove_reference_t< T > && mv ( T && t )

inlinenoexcept

Alias for std::move with a concise syntax.

Template Parameters

T	Type of the value to move.

Parameters

t	Value to move.

Returns

Value cast to an rvalue reference (std::remove_reference_t<T>&&).

fwd() [1/2]

template<typename T>

T && fwd ( std::remove_reference_t< T > & t )

inlinenoexcept

Alias for std::forward with a concise syntax (lvalue overload).

Template Parameters

T	Type to forward.

Parameters

t	Lvalue reference to forward.

Returns

Forwarded reference, preserving value category and const/volatile qualifiers of T.

fwd() [2/2]

template<typename T>

T && fwd ( std::remove_reference_t< T > && t )

inlinenoexcept

Alias for std::forward with a concise syntax (rvalue overload).

Template Parameters

T	Type to forward.

Parameters

t	Rvalue reference to forward.

Returns

Forwarded reference, preserving value category and const/volatile qualifiers of T.