< Krita
Revision as of 02:13, 15 October 2015 by Miabrahams (talk | contribs) (Write about rvalue references)
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General links to about using C++11

There have been a few links discussing mixing C++11 with Qt, and starting with Qt 5.6 C++11 support will be default. Note: as would be expected from those interested in hot new technology, the writers of most of these links demonstrate Silicon Valley levels of extreme optimism. Take this with a grain of salt: there is no such thing as a free lunch.

Particular Features

Under "drawbacks," every item should list: "Programmers will face another feature they must learn about."

Type Inference (auto)

Motivation:

Drawbacks:

Recommendation:

Range-based for loop

Motivation:

Drawbacks: Warning: c++11 range-based for may be slower

Recommendation:

General Initializer Lists

Motivation: Member Initializers Mixed uniform initialization

Drawbacks:

Recommendation:

Lambdas

Motivation: Lambda expressions for slots "C++11 lambdas are your friend"

Drawbacks:

Recommendation:

constexpr

Motivation: Can speed things up inside hot loops. KDAB: speed up your Qt 5 programs using C++11

Drawbacks:

Recommendation:

Override and final

Motivation:

Drawbacks:

Recommendation:

<algorithm>

Motivation:

Drawbacks:

Recommendation:

enum class

Motivation:

Drawbacks:

Recommendation:

nullptr

Motivation:

Drawbacks:

Recommendation:

Deleted and default class members

Motivation:

Drawbacks:

Recommendation:

unique_ptr

Motivation:

Drawbacks: unique_ptr is unable to be copied, and therefore cannot be used inside Qt classes. For example QVector<std::unique_ptr> is invalid, because QVector requires its members can be copied. This makes converting to unique_ptr a bit slow, since QVector<T *> will have to be converted to std_array<unique_ptr<T*>>. If the owner was being copied before, it will become uncopiable. This can be a good thing, but it is work.

Recommendation:

Performance-related (rvalues)

Using move constructors and rvalues are very subtle and advanced features, but widely celebrated as successes of C++11. In general these should be used inside hot paths and when we sling around objects from place to place. C++ programmers should already be aware that writing performant code inside hot paths will sometimes require slinging around ampersands. These features will naturally stay confined to the corners of the codebase where they belong, and should be introduced when they are useful.

Move Constructors

Motivation:

Drawbacks:

Recommendation:

Reference Qualifiers

Motivation:

Drawbacks:

Recommendation:

C++11 features mostly for template programming

Krita makes very light use of templates. These features are useful, coming across them in the code base will add complexity for new learners, and have not been necessary so far.

  • decltype
  • static_assert
  • std::function and std::bind
  • variadic templates

Other C++11 features that probably cannot be used

  • Threads (Qt/KDE use an incompatible threading model)
  • shared_ptr and weak_ptr (Relies on C++ threading model; use KisSharedPointer)
  • New literal types (already have QString)
  • Extended Unions (already have QVariant)

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