[swift-users] Unsafe(Mutable)Pointer (suc)predecessor and advancedBy functions

[Adrian Zubarev]

I’ve got one more questions about Unsafe(Mutable)Pointer. I know that I’m able to access memory that might not belong to me.

My question is:

Can I trust these functions that they will return a pointer to some memory when I allocate more than one object AND when I’m moving only inside that range?

public func successor() -> UnsafeMutablePointer<Memory>
public func predecessor() -> UnsafeMutablePointer<Memory>
public func advancedBy(n: Int) -> UnsafeMutablePointer<Memory>
UnsafeMutablePointer<Int>.alloc(4) when I advance only in range of [0,1,2,3] am I safe or could I get a pointer to memory that does not belong to me?

Example:

// imagine this is some memory portion,
// where x is memory that does not belong to me
// and 0 is moemory free to use
     
[…, x, 0, 0, 0 x, 0, x, …]
     
// now I want to allocate 4 objects  
// variant A:
     
[…, x, MY1, MY2, MY3, x, MY4, x, …]
     
// my pointer will sit at `MY1` and if I advance by 2 I'll get `x`
// can this happen to me?
     
// variant B:
// Unsafe(Mutable)Pointer will ensure that I always get memory tied together  
// (or the above functions will skip memory that doesn't belong to me??):
     
     
[…, x, MY1, MY2, MY3, MY4 x, …]  
So which is right?



-- 
Adrian Zubarev
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