µReact

µReact is an open-source minimalistic single-header reactive programming library for C++11.

❗️ This library is a work-in-progress. It should not be considered release quality yet and its API might still change.
However, it works perfectly fine and can be already used with small future changes in mind.
Feedback is strongly required and appreciated to stabilize the API and achieve the first major release.

Documentation

Features

Update minimality: nothing is re-calculated or processed unnecessarily
Glitch freedom: no transiently inconsistent data sets
Externally synchronized (not thread-safe) by design: it allows not to pay for what you don't use and to have very determined consistent behaviour
Ease of use: small self-contained single header code base, no external dependencies, permissive MIT license
Really easy to get started: it's just 1 header file - see the tutorial
Reliability: the library has an extensive set of tests
Portability: continuously tested under Windows, MacOS and Ubuntu using MSVC/GCC/Clang
Clean warning-free codebase even on the most aggressive warning levels for MSVC/GCC/Clang
Doesn't pollute the global namespace (everything is in namespace ureact) and doesn't drag any headers with it

Examples

Basic usage (run)

ureact::context ctx;

// Declaring reactive variables. We can reassign their values later
ureact::var_signal<int> b = ctx.make_var(1);
ureact::var_signal<int> c = ctx.make_var(2);

// Declaring reactive signal using overloaded operator
// Its value will be updated each time its dependencies are changed
ureact::signal<int> a = b + c;

std::cout << "a (init): " << a.value() << "\n"; // 3

// Assign a new value to 'b'. Value of 'a' is recalculated automatically
b <<= 10;
std::cout << "a  (new): " << a.value() << "\n"; // 12

Complex signals (run)

ureact::context ctx;

ureact::var_signal<int> base = ctx.make_var(1);
ureact::var_signal<int> exp = ctx.make_var(3);

// Declaring reactive signal with formula
// Its value will be recalculated according to the given function
ureact::signal<double> result = make_signal( with(base, exp) , std::pow<int, int> );

// Alternative form of make_signal using operator ->*
ureact::signal<std::string> expression = with(base, exp, result) ->*
    []( int base, int exp, int result ){
        return std::to_string(base) + "^" + std::to_string(exp)
            + " == " + std::to_string(result);
    };

std::cout << expression.value() << "\n"; // 1^3 == 1

base <<= 2;
std::cout << expression.value() << "\n"; // 2^3 == 8

exp <<= 0;
std::cout << expression.value() << "\n"; // 2^0 == 1

Observers (run)

ureact::context ctx;

ureact::var_signal<int> a = ctx.make_var(1);
ureact::signal<int> abs_a = with(a) ->* [](int a){ return std::abs(a); };
ureact::signal<int> abs_a_x2 = abs_a * 2;

// Declaring reactive observers
// They execute given functor only when the observed value is changed
observe(a,        []( int a ){        std::cout << "  a -> "        << a << "\n"; });
observe(abs_a,    []( int abs_a ){    std::cout << "  abs(a) -> "    << abs_a << "\n"; });
observe(abs_a_x2, []( int abs_a_x2 ){ std::cout << "  abs(a)*2 -> " << abs_a_x2 << "\n"; });

// All values change their values so all of them is notified
std::cout << "a <<= 3\n";
a <<= 3;

// Only change of 'a' is notified
// Value of 'abs_a' is not changed after recalculation, so it is not notified
// Value 'abs_a_x2' is not even recalculated because the value of 'abs_a' is not changed
std::cout << "a <<= -3\n";
a <<= -3;

Output:

a <<= 3
  a -> 3
  abs(a) -> 3
  abs(a)*2 -> 6
a <<= -3
  a -> -3

Transaction (run)

ureact::context ctx;

ureact::var_signal<int> b = ctx.make_var(1);
ureact::var_signal<int> c = ctx.make_var(1);
ureact::signal<int> a = b + c;

observe(a, []( int a ){ std::cout << "  a -> " << a << "\n"; });

// Normally values are recalculated each change of their dependencies
std::cout << "without transaction\n";
std::cout << "b <<= 2\n";
b <<= 2;
std::cout << "c <<= 2\n";
c <<= 2;

// To perform several changes atomically they should be grouped into a transaction
std::cout << "\nwith transaction\n";
ctx.do_transaction([&]()
{
    std::cout << "b <<= 3\n";
    b <<= 3;
    std::cout << "c <<= 3\n";
    c <<= 3;
});

Output:

without transaction
b <<= 2
  a -> 3
c <<= 2
  a -> 4

with transaction
b <<= 3
c <<= 3
  a -> 6

See other examples at the examples folder.

License

The class is licensed under the MIT License:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

This software started as a fork of the cpp.react by Sebastian Jeckel (schlangster@gmail.com), BSL 1.0 licensed.

Used third-party tools

The library itself consists of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!

CMake for build automation
ClangFormat for automatic source code indentation
gersemi for automatic CMake code indentation
doctest for the unit tests

Contact