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// Written in the D programming language.
/**
Source: $(PHOBOSSRC std/experimental/allocator/building_blocks/null_allocator.d)
*/
module std.experimental.allocator.building_blocks.null_allocator;
/**
`NullAllocator` is an emphatically empty implementation of the allocator
interface. Although it has no direct use, it is useful as a "terminator" in
composite allocators.
*/
struct NullAllocator
{
import std.typecons : Ternary;
nothrow @nogc pure @safe:
/**
`NullAllocator` advertises a relatively large _alignment equal to 64 KB.
This is because `NullAllocator` never actually needs to honor this
alignment and because composite allocators using `NullAllocator`
shouldn't be unnecessarily constrained.
*/
enum uint alignment = 64 * 1024;
// /// Returns `n`.
//size_t goodAllocSize(size_t n) shared const
//{ return .goodAllocSize(this, n); }
/// Always returns `null`.
void[] allocate(size_t) shared { return null; }
/// Always returns `null`.
void[] alignedAllocate(size_t, uint) shared { return null; }
/// Always returns `null`.
void[] allocateAll() shared { return null; }
/**
These methods return `false`.
Precondition: $(D b is null). This is because there is no other possible
legitimate input.
*/
bool expand(ref void[] b, size_t s) shared
{ assert(b is null); return s == 0; }
/// Ditto
bool reallocate(ref void[] b, size_t) shared
{ assert(b is null); return false; }
/// Ditto
bool alignedReallocate(ref void[] b, size_t, uint) shared
{ assert(b is null); return false; }
/// Returns `Ternary.no`.
Ternary owns(const void[]) shared const { return Ternary.no; }
/**
Returns `Ternary.no`.
*/
Ternary resolveInternalPointer(const void*, ref void[]) shared const
{ return Ternary.no; }
/**
No-op.
Precondition: $(D b is null)
*/
bool deallocate(void[] b) shared { assert(b is null); return true; }
/**
No-op.
*/
bool deallocateAll() shared { return true; }
/**
Returns `Ternary.yes`.
*/
Ternary empty() shared const { return Ternary.yes; }
/**
Returns the `shared` global instance of the `NullAllocator`.
*/
static shared NullAllocator instance;
}
nothrow @nogc pure @safe unittest
{
alias a = NullAllocator.instance;
assert(a.alignedAllocate(100, 0) is null);
assert(a.allocateAll() is null);
auto b = a.allocate(100);
assert(b is null);
assert(a.expand(b, 0));
assert(!a.expand(b, 42));
assert(!a.reallocate(b, 42));
assert(!a.alignedReallocate(b, 42, 0));
assert(a.deallocate(b));
assert(a.deallocateAll());
import std.typecons : Ternary;
assert(a.empty == Ternary.yes);
assert(a.owns(null) == Ternary.no);
void[] p;
assert(a.resolveInternalPointer(null, p) == Ternary.no);
}
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