Streams

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C++ 中的懒惰求值 - http://jscheiny.GitHub.io/Streams/

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工具介绍

C++ 中的懒惰求值 - http://jscheiny.GitHub.io/Streams/

C++ Streams

Streams is a C++ library that provides lazy evaluation and functional-style transformations on the data, to ease the use of C++ standard library containers and algorithms. Streams support many common functional operations such as map, filter, and reduce, as well as various other useful operations such as various set operations (union, intersection, difference), partial sum, and adjacent difference, as well as many others.

To use, simply #include "Stream.h", and compile using a C++14 compatible compiler. All streams classes/functions can be found in the stream namespace.

Links:

Examples

Coin flip experiment:

cpp

using namespace stream;
using namespace stream::op;

int number_heads(int flips) {
    return MakeStream::coin_flips()
        | limit(flips)
        | filter()
        | count();
};

void experiment(int trials, int flips) {
    auto stats = MakeStream::generate(std::bind(number_heads, flips))
        | limit(trials)
        | reducers::SummaryStats().reducer();
    std::cout  ");
    std::cout  12 -> 6 -> 3 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1

Vector operations:

cpp

std::vector x = /* ... */;
std::vector y = /* ... */;

auto to_stream = [](std::vector& vec) {
    return MakeStream::from(vec);
};

std::vector sum_vec = to_stream(x) + to_stream(y);
std::vector diff_vec = to_stream(x) - to_stream(y);
double dot_product = (to_stream(x) * to_stream(y)) | sum();
std::vector scaling = to_stream(x) * 10;
std::vector translating = to_stream(x) + 3.7;

Set operations:

cpp

std::set x = /* ... */;
set::set y = /* ... */;

auto to_stream = [](std::set& vec) {
    return MakeStream::from(vec);
};

std::set set_union = to_stream(x) | union_with(to_stream(y));
// Better than:
//   std::set result;
//   std::set_union(x.begin(), x.end(), y.begin(), y.end(),
//                  inserter(result, result.end()));
std::set set_intersect = to_stream(x)
    | intersection_with(to_stream(y));
std::set set_diff = to_stream(x)
    | difference_with(to_stream(y));
std::set set_sym_diff = to_stream(x)
    | symmetric_difference_with(to_stream(y));

Adding unique ids:

cpp

std::vector objects = /* ... */;

std::vector objects_with_ids = MakeStream::from(objects)
    | zip_with(MakeStream::counter(1), [](T&& object, int id) {
        object.set_id(id);
        return object;
    });

Printing containers:

cpp

(MakeStream::from(container) | print_to(std::cout)) (tup) % n == 0; })
         | map_([](auto&& tup) { return std::get(tup); });
};

MakeStream::from({1, 3, 8, 4, 7}) | every_nth(2) | print_to(std::cout); // 1 8 7