If I correctly read the code – all the versions of boolinq::from copy provided container to the TC field of the IteratorContainerPair. Is this design intentional? Because it could be rather expensive on large collections.

Also, won't simple code like this do:

template <typename Container>
LinqObject<... smth. with decltype(std::begin(containter) ...> from(
         const Container& container) {
    return from(std::begin(container), std::end(container));
}

?

Add C++11, C++14, C++17, C++20 to Travis-CI Matrix.

You can make boolinq-test to be compiled with all this standards. Remember that target boolinq-test14 is not compatible with C++11.

So if orderby descending an array [3, 2, 5, 4, 1] would result: [5, 4, 3, 2, 1]

can‘t be caught by std::exception &

Current CI/CD Pipeline

The current project simply uses TravisCI to run builds and tests for all PRs and branches in this repository. As defined in the current .travis.yml, all builds take place in a single environment:

• Arch: X64 | OS: Ubuntu 16.04.7 LTS (Xenial Xerus)

This environment is used to build boolinq with the following compilers:

• clang (v3.8)
• g++ (v5-v9)
• gcc (v5-v9)

Next Steps

Tracked by Issues: #64 & #63, efforts are being made to support the windows C++ compiler msvc, add the AppVeyor CI tool and build with different C++ standards. These changes to the project require a closer look at the entire CI/CD pipeline, as questions remain unclear:

• "Which CI tool should run which OS?"
• "What type of architectures should be supported?"
• "How should builds be tracked in GitHub?"

This issue may act as a medium for discussion regarding questions and proposals to the CI/CD pipeline of this project.

Hello.

With c++11 there is an compile error. Adding "#include <algorithm>" error disappeared.
Could you add this header include?

In file included from /home/nickfox/Desktop/jfxrender/include/jfxmaterial.h:8:0,
                 from /home/nickfox/Desktop/jfxrender/src/jfxmaterial.cpp:1:
/home/nickfox/Desktop/jfxrender/submodule/boolinq/include/boolinq/boolinq.h: In member function ‘boolinq::Linq<std::tuple<std::vector<T, std::allocator<_T2> >, _TIter, bool>, T> boolinq::Linq<S, T>::orderBy(F) const’:
/home/nickfox/Desktop/jfxrender/submodule/boolinq/include/boolinq/boolinq.h:337:18: error: ‘sort’ is not a member of ‘std’
             std::sort(items.begin(), items.end(), [transform](const T &a, const T &b) {
                  ^~~~
/home/nickfox/Desktop/jfxrender/submodule/boolinq/include/boolinq/boolinq.h:337:18: note: suggested alternative: ‘set’
             std::sort(items.begin(), items.end(), [transform](const T &a, const T &b) {
                  ^~~~
                  set

First of all, thanks for the awesome library!
I do have question about Grouping. In C#, I able to group a collection with multiple keys via anonymous object, here's an example:
https://github.com/SirusDoma/O2MusicBox/blob/master/Source/CXO2/Processors/Encoders/O2Jam/OJNEncoder.cs#L38

In above example, I'm using anonymous object from 3 properties of the original object. I'm now wondering, is it possible to do the same thing with boolinq?

At best this might be called "LINQ like API", probably.

Hello there,
first of all, I have a big compliment to offer. Wonderful work. 👍

I wanted to use boolinq on my current platform.io esp32 project. However, I always get the following error when using select:

no instance of function template "boolinq::Linq<S, T>::select [with S=std::tuple<boolinq::Linq<std::pair<const int *, const int *>, int>, int>, T=int]" matches the argument list -- argument types are: (lambda []int (int a)->int) -- object type is: boolinq::Linq<std::tuple<boolinq::Linq<std::pair<const int *, const int *>, int>, int>, int>

Using the example from the readme.

using namespace boolinq;

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();

is this due to the compiler used by platform.io? Do I have to include the file differently?

Thanks for your help.
Greetings
Ruffo

Figure out why it is not working anymore and fix it in a separate PR.

This select lambda argument type in this test looks insane:

1. Extract this test to separate target test14 (create it) or something and configure it to use C++14 and use auto instead of this long type.
2. Add this example to README, specify that C++14 is required to use auto here.

I propose to reorganize the project structure.

From:

..
|__benchmark
|
|__boolinq
   |__*Test.cpp
   |__SpeedTest.cpp
   |__boolinq.h

To something like (for instance):

..
|__externals            (Third party tools)
|  |__benchmark
|
|__test                 (Test suites)
|  |__*Test.cpp
|
|__include              (Source code)
|  |__boolinq
|     |__boolinq.h
|
|__benchmark            (Benchmarks)
   |__SpeedTest.cpp

The main idea is make tests, benchmarks and source code separate.

I've been using C# and LINQ for years, so this library looks just fantastic, as I am using C++ now and really miss how expressive C# is.

I run this example code:

int src[] = {1,2,3,4,5,6,7,8};
std::vector<int> dst = boolinq::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();

I get an exception in this function:

////////////////////////////////////////////////////////////////
// Linq Creators
////////////////////////////////////////////////////////////////

template<typename T>
Linq<std::pair<T, T>, typename std::iterator_traits<T>::value_type> from(const T & begin, const T & end)
{
    return Linq<std::pair<T, T>, typename std::iterator_traits<T>::value_type>(
        std::make_pair(begin, end),
        [](std::pair<T, T> &pair) {
            if (pair.first == pair.second) {
                throw LinqEndException();
            }
            return *(pair.first++);
        }
    );
}

The exception is on this line:

return *(pair.first++);

The exception is:

Exception thrown at 0x00007FFB4A13A388 in DemoRange.exe: Microsoft C++ exception: boolinq::LinqEndException at memory location 0x000000807813CCF4.

Environments tried in:

MSVC 2017 15.9.16 + MSVC with "ISO C++17 Standard (/std:c++17)"
MSVC 2017 15.9.16 + Intel Compiler v19.0 

boolinq.h:67: Warning: C4100: 'index': unreferenced formal parameter

Here is source code, pls fix. Also, there are some other unreferences local variables/parameters which also produce these warnings.

        void for_each(std::function<void(T)> apply) const
        {
            return for_each_i([apply](T value, int index) { return apply(value); });
        }

Привет. Нет возможности проверить, но очень интересно.

В примерах увидел, что везде цепочка вызовов заканчивается toVector to...

А можно написать как то так

for(auto&& i : from({1,2,3})
.where([] (auto&& i) {
return i % 2 == 0;
}))
Что то делаем...

auto enumerable = from(...).where(...)
Не будет вычисляться до того момента пока не сделаем функцию to...? Или не начнём итертровать? Как в дот нет? Спасибо

Is it possible to return a NULL, or perhaps a predefined string, instead of NaN when no records are found?

Attempting to retrieve data that does not exist does not feel like exceptional behaviour to me.

Thanks

Hi,

How can I selectMany with objects? For example:

auto concatInnerList =
    from(*myObj)
        .selectMany([](const MyObj& myObjTemp) { return myObjTemp.innerList; })
        .toStdArray();

myObj is a std::vector<MyObject> which contains an inner list object std::vector.

Is there a list of requirements to make custom containers compatible with this library? I've implemented (c)begin/(c)end and most of everything I need for stl compatibility but don't know what boolinq requires.

Since this is a C++ header, shouldn’t <climits> be included instead of <limits.h> at the third line?

Is it possible to groupBy, and then return the average for each group?

for example, this SQL query?

SELECT name, day, avg(time_on_phone) FROM data
GROUP BY name, day;

It would be great to be able to give an actual value to firstOrDefault to return when there is no first element. Right now it returns T(), which is not always desirable, and it would be great if there was an overload that takes a T&& or T const& and returns that instead.

I am using your library. It could be built with C++ 17. But now I've changed my projects to be built with C++ 20 and it gives errors. Simple example error is like that:

int main() {
	vector<int> asd = { 3, 4, 1, -1, 565 };
	for (int b : from(asd).where([](int a) { return a > 3; }).toStdVector())
		cout << b << endl;

	return 0;
}

Severity	Code	Description	Project	File	Line	Suppression State
Error (active)	E0135	class "boolinq::Linq<std::tuple<boolinq::Linq<std::pair<std::_Vector_const_iterator<std::_Vector_val<std::conditional_t<true, std::_Simple_types<int>, std::_Vec_iter_types<int, size_t, ptrdiff_t, int *, const int *, int &, const int &>>>>, std::_Vector_const_iterator<std::_Vector_val<std::conditional_t<true, std::_Simple_types<int>, std::_Vec_iter_types<int, size_t, ptrdiff_t, int *, const int *, int &, const int &>>>>>, int>, int>, int>" has no member "toStdVector"

This will not work:

std::vector<std::unique_ptr<MyType>> myVector;
boolinq::from(xmlLogicFragments)
    .select([](const auto& uniquePtr) { return uniquePtr.get(); })
    .toVector();

I.e. conversion from the vector of the unique ptrs to the vector of raw ptrs does not work.
The vector of unique ptrs is convenient to have RAII for the collection of items, as it is suggested e.g. here http://stackoverflow.com/questions/27460377/why-is-using-vector-of-pointers-considered-bad

Also there are possible the other situations, when non-copyable elements can be used.

Would that be possible if boolinq is working with the references to the elements in such cases instead?

Hello,

Since this states it supports the map stl container type, and if this is supposed to mimic C# Linq, then I think its reasonable to expect that there should be a ToDictionary() equivalent (toMap() for C++/boolinq).

I don't fully understand C++ templates (does anyone, really?) but I was able to put together a basic implementation. The implementation takes two selector functions, one for key, another for value, just like Linq's ToDictionary( ) in C#.

Implementation code:

#include <map>   //remember to include map

template<typename F, typename _FRet = typename priv::result_of<F(T)>::type,
              typename G, typename _GRet = typename priv::result_of<G(T)>::type>
     std::map<_FRet, _GRet> toMap(F keySelector, G valueSelector) const
     {
         auto keys = select_i([keySelector](T value, int /*index*/)
         { 
             return keySelector(value); 
         }).toStdVector();

         auto values = select_i([valueSelector](T value, int /*index*/)
         { 
             return valueSelector(value); }
         ).toStdVector();
         
         std::map< _FRet, _GRet> toReturn;
          
         for (int i = 0; i < keys.size(); i++)
         {
             toReturn[keys[i]] = values[i];
         }

         return toReturn;
     }

One key difference (pun intended) is that this version does not throw an exception if they keys are not distinct, it just overwrites duplicate values in the loop. I do not need such a behavior for my purposes but it could be modified to mimic this as well.

Example usage:

        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},
	};
 
        auto resultMap = 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; })
          };
	}).toMap( [](const Tax& a) {return a.name; }, //key selector
	                [](const Tax& a) {return a.amount_1; });//value selector
        
        int value = resultMap["tax 1"];
        cout << value;

I am using Qt 5.15.2. Compiling with msvc 2019 64 bit giving so many error. Is there any way?

I really like this implementation, but I don't know how to solve this:

struct Tax {
    std::string name;
    int amount_1;
    int amount_2;
    int amount_3;
};

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

The result that I expect would be a vector with these values, where for each tax.name the corresponding amounts are added

Dump result vector

"tax 1", 7, 7
"tax 2", 1, 1
"tax 3", 3, 3

Thanks in advance !

We need Ranges to allow modification items during enumeration. We need to investigate can this be achieved in the same syntax:

from(items).for_each([](Human & human){human.age += 1;})

or requires different constructors like:

mut_from(items).for_each([](Human & human){human.age += 1;})

The same question about unexpectedly producing copies - this should not happen actually. Or maybe we need a separate constructor for this:

int total = 0;
copy_from(items).for_each([](Human human){total += human.age;})

Plan:

1. Checkout these issues: #22, #44
2. I started experimenting with this here a while ago: #29
3. Propose the best solution :)

Investigate and propose solution to make the library extremely useful. Prefer implicit over explicit mutability and copy-ability specification.

Hello! Every next call do a copy, how to pass a ref value?

Example:

struct test_t {
    std::string v1;
    int         v2;
};
constexpr std::size_t benchmarkVectorSize{ 1000000 };
std::vector<test_t> vecCpp(benchmarkVectorSize);

srand(0xDEADBEEF);

for (unsigned i = 0; i < benchmarkVectorSize; i++) {
    const auto x = rand();
    vecCpp[i].v2 = x;
    vecCpp[i].v1 = std::to_string(x);
}
boolinq::from(vecCpp).for_each([](test_t a) {
    a.v1;
    int iii = 02;
});

every for_each make object copy about 2 times
how to aviod this, and how can i change value in for_each ops;

I want this work well:

boolinq::from(vecCpp).for_each([](test_t &a) {
    a.v1 = "123"
});

Figure out what is necessary and what is not, make this project clean and simple again.

You say that there is "Qt collections", what exactly this means? Any examples?

can you add this method ?

We need AppVeyor build matrix to support at least 2 axis:

1. Different C++ compilers (gcc, clang, msvc) with different major versions
2. Different C++ standards: C++11, C++14, C++17, C++20 (boolinq-test14 is not compatible with C++11)

class Product{
public:
QString name;
QString no;
double quantity;
double price;
bool operator ==(const Product& pro) const {
return no.compare(pro.no) == 0;
}
};

Product pro1;
pro1.no = "1";
pro1.quantity= 1;
pro1.price= 10 ;
pro1.name= "1. Product";

Product pro2;
pro2.no = "2";
pro2.quantity= 2;
pro2.price= 20;
pro2.name= "2. Product";

Product pro3;
pro3.no = "1";
pro3.quantity= 1;
pro3.price= 10 ;
pro3.name= "1. Product";

QList list;
list.append(pro1);
list.append(pro2);
list.append(pro3);

auto dst = boolinq::from(list)
.groupBy([](const Product & a){return a.no;})
.select([](const auto & pair){
Product pro;
pro.no= pair.first;
pro.quantity= pair.second.sum([](const Product & a){return a.quantity;});
pro.price= pair.second.sum([](const Product & a){return a.price;});
pro.name = ???? // ****** here how to access name variable of Product class ********************
return pro;

       }).toStdList();

I know this is only a question not an issue. I have no any opportunity.