C++React is reactive programming library for C++11.
Generally speaking, it provides abstractions to handle change propagation and data processing for a push-based event model. A more practical description is that it enables coordinated, multi-layered - and potentially parallel - execution of callbacks. All this happens implicitly, based on declarative definitions, with guarantees regarding
- update minimality - nothing is re-calculated or processed unnecessarily;
- glitch freedom - no transiently inconsistent data sets;
- thread safety - no data races for parallel execution by avoiding side effects.
The core abstractions of the library are
- signals, reactive variables that are automatically re-calculated when their dependencies change, and
- event streams as composable first class objects.
Signals specifically deal with aspects of time-varying state, whereas event streams facilitate event processing in general.
Additional features include
- a publish/subscribe mechanism for callbacks with side effects;
- a set of operations and algorithms to combine signals and events;
- a domain model to encapsulate multiple reactive systems;
- transactions to group related events, supporting both synchronous and asynchrounous execution.
If you're interested in learning about C++React, have a look at its documentation.
This library is a work-in-progress. It should not be considered release quality yet and its API might still change. It is, however, in a perfectly usable state and has already received a fair amount of testing and tuning.
- Intel TBB 4.2 (required)
- Google test framework (optional, to compile the unit tests)
- Boost 1.55.0 C++ Libraries (optional, to include Reactor.h, which requires
boost::coroutine)
C++React has been tested with the following compilers:
- Visual Studio 2013.2
- GCC 4.8.2
- Clang 3.4
To build with Visual Studio, use the pre-made solution found in project/msvc/.
To build with GCC or Clang, use CMake:
mkdir build
cd build
cmake ..
make
For more details, refer to the Build instructions.
Signals are self-updating reactive variables. They can be combined in expressions to create new signals, which are automatically re-calculated when their dependencies change.
using namespace std;
using namespace react;
// Defines a reactive domain that uses single-threaded, sequential updating
REACTIVE_DOMAIN(D, sequential)
// Defines aliases for types of the given domain,
// e.g. using VarSignalT<X> = VarSignal<D,X>
USING_REACTIVE_DOMAIN(D)
// Two reactive variables that can be manipulated imperatively
// to input external changes
VarSignalT<int> width = MakeVar<D>(1);
VarSignalT<int> height = MakeVar<D>(2);
// A signal that depends on width and height and multiplies their values
SignalT<int> area = MakeSignal(
With(width, height),
[] (int w, int h) {
return w * h;
});Signal values can be accessed imperatively:
cout << "area: " << area.Value() << endl; // => area: 2
// Width changed, so area is re-calculated automatically
width.Set(10);
cout << "area: " << area.Value() << endl; // => area: 20Or, instead of using Value() to pull the new value, callback functions can be registered to receive notifications on a change:
Observe(area, [] (int newValue) {
cout << "area changed: " << newValue << endl;
});Overloaded operators for signal types allow to omit MakeSignal for a more concise syntax:
// Lift as reactive expression - equivalent to previous example
SignalT<int> area = width * height;Unlike signals, event streams are not centered on changing state, but represent flows of discrete values. They are first-class objects and can be merged, filtered, transformed or composed to more complex types:
using namespace std;
using namespace react;
REACTIVE_DOMAIN(D, sequential)
USING_REACTIVE_DOMAIN(D)
// Two event sources
EventSourceT<Token> leftClick = MakeEventSource<D>();
EventSourceT<Token> rightClick = MakeEventSource<D>();
// Merge both event streams
EventsT<Token> anyClick = leftClick | rightClick;
// React to events
Observe(anyClick, [] (Token) {
cout << "clicked!" << endl;
});leftClick.Emit(); // => clicked!
rightClick.Emit(); // => clicked!
When enabling it through the concurrency policy, updates are automatically parallelized:
REACTIVE_DOMAIN(D, parallel)
VarSignalT<int> in = MakeVar<D>(0);
SignalT<int> op1 = MakeSignal(in,
[] (int in) {
int result = doCostlyOperation1(in);
return result;
});
SignalT<int> op2 = MakeSignal(in,
[] (int in) {
int result = doCostlyOperation2(in);
return result;
});
// op1 and op2 can be re-calculated in parallel
SignalT<int> out = op1 + op2;The API of C++React has been inspired by the following two research papers: