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1467. Deriving atomic<T*> from atomic_address breaks type safety

Section: 99 [atomics.types.address] Status: Resolved Submitter: INCITS Opened: 2010-08-25 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Addresses US-163

Requiring atomic<T*> to be derived from atomic_address breaks type safety: 

atomic<double*> ip;
char ch;
atomic_store(&ip, &ch);
*ip.load() = 3.14159;

The last line overwrites ch with a value of type double.

[ 2010-10-27 Daniel adds: ]

Resolving this issue will also solve 1469(i)

Accepting n3164 would solve this issue by removing atomic_address.

[ Resolved in Batavia by accepting n3193. ]

Proposed resolution:

  1. Change 32.5.8 [atomics.types.generic], class template specialization atomic<T*> synopsis, as indicated: 
    namespace std {
  template <class T> struct atomic<T*> : atomic_address {
    [..]
  };
  [..]
}
  2. Change 32.5.8 [atomics.types.generic] p. 4 as indicated:

    4 There are pointer partial specializations on the atomic class template. These specializations shall be publicly derived from atomic_address. The unit of addition/subtraction for these specializations shall be the size of the referenced type. These specializations shall have trivial default constructors and trivial destructors.