Description:

template<typename T, typename TAllocator>
struct alib::lang::StdAllocator< T, TAllocator >

This struct is an implementation of C++ standard library type std::allocator. It is to be used with container types provided by the C++ standard library in combination with ALib Allocators.

With the inclusion of module ALib Monomem in the ALib Build, this allocator is suitable to use cases of strict or weak monotonic allocation.

Shortcuts for Specific ALib Allocators

The following alias type definitions exist for this type, each addressing a specific allocator:

StdMA, and
StdPA.

Along with this, shortcuts to the container types are likewise provided with:

Resetting A Container

While the dedicated container types provided with module ALib Containers offer a method named Reset (see, for example, HashTable::Reset), the C++ standard containers do not. This is a challenge because their internal memory will be invalid with a reset. For example, if allocator type MonoAllocator was used with class std::vector, there is no interface method that makes the vector "forget" its internal data array. Its method shrink_to_fit by its specification is not forced to shrink anything or even dispose the data if the size was 0 when called. This is implementation-dependent.

The way out is as simple as radical: The container is just to be destructed and reconstructed "in place". This can be done using a C++ placement-new. The following code snippet demonstrates this:

// field members  or global objects
alib::MonoAllocator allocator( ALIB_DBG("MyAllocator",)  4);
std::vector<MyData, StdMA<MyData>> transactionObjects( allocator );
 
// method using the allocator and the vector
void processTransaction( /* transaction data */)
{
    // perform transaction, collecting stuff in vector and/or allocator
    // ...
    // ...
    // ...
 
    // before we leave we reset the vector and the allocator:
 
    // 1. Destruct the container and contained objects.
    //    (In case contained objects are trivially destructible, this is not
    //    needed and usually optimized out by the compiler.)
    allocator().Delete(&transactionObjects);
 
    // 2. Reset allocator
    allocator.Reset();
 
    // 3. Placement new on the vector object
    new( &transactionObjects ) std::vector<MyData, StdMA<MyData>>( allocator );
}
 

See also

An alternative version that recycles nodes (and also bucket arrays in case of std::unordered_set and std::unordered_map), is provided with sibling type StdRecyclingAllocator.
Type definitions StdMA and StdPA given with module ALib Monomem.
Further shortcuts for standard container types, given with StdVectorMA, StdVectorPA, StdListMA, StdListPA, StdDequeMA, and StdDequePA.

Template Parameters

T	The type of objects to be allocated.
TAllocator	The allocator type, as prototyped with Allocator.

Definition at line 758 of file allocation.inl.

Inheritance diagram for alib::lang::StdAllocator< T, TAllocator >:

[legend]

Collaboration diagram for alib::lang::StdAllocator< T, TAllocator >:

[legend]

Public Type Index:
using	AllocatorType = TAllocator
	Exposes template parameter TAllocator.

using	allocBase = AllocatorMember<TAllocator>
	The type of the base class that stores the allocator.

using	difference_type = std::ptrdiff_t
	Type definition as required by C++ library standards.

using	propagate_on_container_move_assignment = std::false_type
	Type definition as required by C++ library standards.

using	size_type = std::size_t
	Type definition as required by C++ library standards.

using	value_type = T
	Type definition as required by C++ library standards.

Public Type Index: inherited from alib::lang::AllocatorMember< TAllocator >
using	AllocatorType = TAllocator
	Exposes the allocator type.

Public Method Index:
constexpr	StdAllocator () noexcept=default
	Parameterless constructor used with heap allocation.

constexpr	StdAllocator (const StdAllocator &) noexcept=default
	Defaulted copy constructor.

template<typename TSibling>
	StdAllocator (const StdAllocator< TSibling, TAllocator > &origin)

template<typename TSibling> requires alib::lang::IsAllocator<typename TSibling::allocator>
constexpr	StdAllocator (const TSibling &origin) noexcept

constexpr	StdAllocator (StdAllocator &&) noexcept=default
	Defaulted move constructor.

constexpr	StdAllocator (TAllocator &pAllocator) noexcept

constexpr	~StdAllocator () noexcept=default
	Parameterless destructor used with heap allocation.

constexpr T *	allocate (size_t n)

constexpr std::allocation_result< T *, std::size_t >	allocate_at_least (std::size_t n)

constexpr void	deallocate (T *p, std::size_t n)

Public Method Index: inherited from alib::lang::AllocatorMember< TAllocator >
template<typename TIf = TAllocator> requires std::is_default_constructible_v<TIf>
	AllocatorMember ()

	AllocatorMember (TAllocator &pAllocator) noexcept

AllocatorInterface< TAllocator >	AI () const noexcept

TAllocator &	GetAllocator () const noexcept

Additional Inherited Members
Protected Field Index: inherited from alib::lang::AllocatorMember< TAllocator >
TAllocator *	allocator
	The allocator stored.

Type Definition Details:

◆ AllocatorType

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::AllocatorType = TAllocator

Exposes template parameter TAllocator.

Definition at line 766 of file allocation.inl.

◆ allocBase

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::allocBase = AllocatorMember<TAllocator>

The type of the base class that stores the allocator.

Definition at line 769 of file allocation.inl.

◆ difference_type

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::difference_type = std::ptrdiff_t

Type definition as required by C++ library standards.

Definition at line 762 of file allocation.inl.

◆ propagate_on_container_move_assignment

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::propagate_on_container_move_assignment = std::false_type

Type definition as required by C++ library standards.

Definition at line 763 of file allocation.inl.

◆ size_type

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::size_type = std::size_t

Type definition as required by C++ library standards.

Definition at line 761 of file allocation.inl.

◆ value_type

template<typename T, typename TAllocator>

using alib::lang::StdAllocator< T, TAllocator >::value_type = T

Type definition as required by C++ library standards.

Definition at line 760 of file allocation.inl.

Constructor(s) / Destructor Details:

◆ StdAllocator() [1/3]

template<typename T, typename TAllocator>

alib::lang::StdAllocator< T, TAllocator >::StdAllocator ( TAllocator & pAllocator )

inlineconstexprnoexcept

Constructor for the initial allocator instantiation.

Parameters

pAllocator The allocator.

Definition at line 777 of file allocation.inl.

◆ StdAllocator() [2/3]

template<typename T, typename TAllocator>

template<typename TSibling>
requires alib::lang::IsAllocator<typename TSibling::allocator>

alib::lang::StdAllocator< T, TAllocator >::StdAllocator ( const TSibling & origin )

inlineconstexprnoexcept

Copy constructor using an instance of a different template type.

Template Parameters

TSibling The originating allocator's type (StdAllocator<X>).

Parameters

origin The originating allocator of type TSibling .

Definition at line 792 of file allocation.inl.

◆ StdAllocator() [3/3]

template<typename T, typename TAllocator>

template<typename TSibling>

alib::lang::StdAllocator< T, TAllocator >::StdAllocator ( const StdAllocator< TSibling, TAllocator > & origin )

inline

Copy constructor using an instance of a different template type.

Template Parameters

TSibling The originating allocator's type (StdAllocator<X>).

Parameters

origin The originating allocator of type TSibling .

Definition at line 799 of file allocation.inl.

Method Details:

◆ allocate()

template<typename T, typename TAllocator>

T * alib::lang::StdAllocator< T, TAllocator >::allocate ( size_t n )

inlinenodiscardconstexpr

Passes the allocation request to the AllocatorMember.

Parameters

n	The number of requested objects to allocate storage for.

Returns: Pointer to the start of the array of n objects of type T.

Definition at line 813 of file allocation.inl.

◆ allocate_at_least()

template<typename T, typename TAllocator>

std::allocation_result< T *, std::size_t > alib::lang::StdAllocator< T, TAllocator >::allocate_at_least ( std::size_t n )

inlinenodiscardconstexpr

The C++23 extension of std::allocator finally supports ALib mechanics of using oversized allocation objects.

Parameters

n	The number of requested objects to allocate storage for.

Returns: The Pointer to the start of the allocated objects of type T as well as the number of objects allocated, which will be equal or higher than n.

Definition at line 823 of file allocation.inl.

◆ deallocate()

template<typename T, typename TAllocator>

void alib::lang::StdAllocator< T, TAllocator >::deallocate	(	T *	p,
		std::size_t	n )

inlineconstexpr

Frees the given array of objects.

Parameters

p	Pointer to the previously allocated memory.
n	The number of objects allocated.

Definition at line 837 of file allocation.inl.

The documentation for this struct was generated from the following file:

allocation.inl

Description:

Shortcuts for Specific ALib Allocators

Resetting A Container

Public Type Index:

Public Method Index:

Additional Inherited Members

Type Definition Details:

◆ AllocatorType

◆ allocBase

◆ difference_type

◆ propagate_on_container_move_assignment

◆ size_type

◆ value_type

Constructor(s) / Destructor Details:

◆ StdAllocator() [1/3]

◆ StdAllocator() [2/3]

◆ StdAllocator() [3/3]

Method Details:

◆ allocate()

◆ allocate_at_least()

◆ deallocate()