[cppcon2016][c++] Leak-Freedom in C++ - note

CppCon 2016 - Herb Sutter “Leak-Freedom in C++... By Default.”-
https://goo.gl/2TNgQI
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• Ensure an object will be destroyed once it is no longer needed.
• Correct by construction!

template<typename T>
using Pimpl = const unique_ptr<T>;
unique_ptr<data[]> ptr;

Double linked list:

• a unique_ptr to the next
• a raw ptr to the back

shared_ptr with alias constructor:

• https://www.justsoftwaresolutions.co.uk/cplusplus/shared-ptr-secret-constructor.html
• Used for passing the leaf of a tree d.s around while keeping the root/tree alive.

• Do not violate layering.
• Don't create ownership cycles across modules by owning 'upward' (violates layering)
• Use weak_ptr to break cycles.

How?

• Don't pass an owner down to 'unknow code' that might store it.
  e.g storing a shared_ptr
• Simple.
  Use weak_ptr inside the call back callable object which point
  to outside resource.

ownership types:

• 1 object, 1 owner:
  unique_ptr
• 1 object , n owners:
  shared_ptr
• N objects, 1 or n owners:
  deffered_ptr

Reachability is a property of the while group.
Not detectable from 1 object, or subgroup.

Idea:
heap for deffered_ptr is isolated.
Each module could have one isolated heap.
github.com/hsutter/gcpp