Region.this

this(ubyte[] store) pure nothrow @nogc

Constructs a region backed by a user-provided store. Assumes the memory was allocated with ParentAllocator.

`store`	User-provided store backing up the region. Assumed to have been allocated with `ParentAllocator`.
`n`	Bytes to allocate using `ParentAllocator`. If `parent.allocate(n)` returns `null`, the region will be initialized as empty (correctly initialized but unable to allocate).