https://github.com/dropbox/nn

Non-nullable pointers for C++
https://github.com/dropbox/nn

Last synced: 18 days ago
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Non-nullable pointers for C++

• Host: GitHub
• URL: https://github.com/dropbox/nn
• Owner: dropbox
• License: apache-2.0
• Archived: true
• Created: 2015-07-07T17:59:21.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2017-06-23T23:32:33.000Z (over 7 years ago)
• Last Synced: 2024-07-31T22:45:15.302Z (3 months ago)
• Language: C++
• Size: 16.6 KB
• Stars: 314
• Watchers: 34
• Forks: 33
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: license.txt

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README

        
# `nn`: Non-nullable pointers for C++

`nn` is a type that helps you enforce at compile time the contract that a given pointer

can't be null. It wraps around raw pointers or smart pointers, and works particularly

well out of the box with `std::unique_ptr` and `std::shared_ptr`.

Here's an example:

```cpp

class Widget : public WidgetBase {

public:

  Widget(nn_shared_ptr gadget) : m_gadget(move(gadget)) {}

  // ...

private:

  nn_shared_ptr m_gadget;

};

// nn_make_unique and nn_make_shared always return non-null values

nn_unique_ptr my_widget = nn_make_unique(nn_make_shared());

// but what if we have a pointer already and we don't know if it's null?

shared_ptr this_might_be_null = ...

my_widget = nn_make_unique(NN_CHECK_ASSERT(this_might_be_null));

// implicit nn_unique_ptr -> nn_shared_ptr works just like unique_ptr -> shared_ptr

nn_shared_ptr shared_widget = move(my_widget);

// the `nn` implicitly casts away if needed

void save_ownership_somewhere(shared_ptr);

save_ownership_somewhere(shared_widget);

// implicit upcasts work too

nn_shared_ptr base_ptr = shared_widget;

```

Compile-time checking helps find bugs sooner. At Dropbox we use `nn` pervasively in our

cross-platform C++ codebase.

## Compatibility

nn is C++11 compatible. Tested with GCC 4.8, clang 3.6+ and MSVS 2015.