qt linq boolinq-526互联

https://github.com/k06a/boolinq

Super tiny C++11 single-file header-only LINQ template library

Just imagine .NET Framework LINQ support for STL/Qt collections :)

Get source code here: boolinq.h

Wanna demo?

Example with integers

int src[] = {1,2,3,4,5,6,7,8};
auto dst = from(src).where( [](int a) { return a % 2 == 1; })      // 1,3,5,7
                    .select([](int a) { return a * 2; })           // 2,6,10,14
                    .where( [](int a) { return a > 2 && a < 12; }) // 6,10
                    .toStdVector();

// dst type: std::vector<int>
// dst items: 6,10

Example with structs

struct Man {
    std::string name;
    int age;
};

Man src[] = {
    {"Kevin",14},
    {"Anton",18},
    {"Agata",17},
    {"Terra",20},
    {"Layer",15},
};

auto dst = from(src).where(  [](const Man & man) { return man.age < 18; })
                    .orderBy([](const Man & man) { return man.age; })
                    .select( [](const Man & man) { return man.name; })
                    .toStdVector();

// dst type: std::vector<std::string>
// dst items: "Kevin", "Layer", "Agata"

Interesting example

struct Message {
    std::string PhoneA;
    std::string PhoneB;
    std::string Text;
};

Message messages[] = {
    {"Anton","Troll","Hello, friend!"},
    {"Denis","Wride","OLOLO"},
    {"Anton","Papay","WTF?"},
    {"Denis","Maloy","How r u?"},
    {"Denis","Wride","Param-pareram!"},
};

int DenisUniqueContactCount =
    from(messages).where(   [](const Message & msg) { return msg.PhoneA == "Denis"; })
                  .distinct([](const Message & msg) { return msg.PhoneB; })
                  .count();

// DenisUniqueContactCount == 2

Test in C++14 using auto

The following test requires C++14 GroupByTestComplex.cpp It uses auto in order to avoid a very long lambda argument type. The return type of a function or lambda expression can be deduced by its operand since C++14. The CMake file is changed so that this test runs with C++14.

TEST(GroupBy, CountTaxes)
{
    struct Tax {
        std::string name;
        int amount_1;
        int amount_2;

        bool operator ==(const Tax & tax) const {
            return name == tax.name
                && amount_1 == tax.amount_1
                && amount_2 == tax.amount_2;
        }
    };

    std::vector<Tax> taxes = {
        {"tax 1", 1, 1},
        {"tax 2", 1, 1},
        {"tax 1", 2, 2},
        {"tax 3", 3, 3},
        {"tax 1", 4, 4},
    };

    Tax ans[] = {
        {"tax 1", 7, 7},
        {"tax 2", 1, 1},
        {"tax 3", 3, 3},
    };

    auto dst = from(taxes)
        .groupBy([](const Tax & a){return a.name;})
        .select([](const auto & pair){ // use of auto here needs c++14
            return Tax {
                pair.first,
                pair.second.sum([](const Tax & a){return a.amount_1;}),
                pair.second.sum([](const Tax & a){return a.amount_2;})
            };
        });

    CheckRangeEqArray(dst, ans);
}