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Questions tagged [boost-hana]

Boost.Hana is a C++14-based metaprogramming library. It provides high level algorithms to manipulate heterogeneous sequences, allows writing type-level computations with a natural syntax, provides tools to introspect user-defined types and much more.

Boost.Hana is a C++14-based metaprogramming library. It provides high level algorithms to manipulate heterogeneous sequences, allows writing type-level computations with a natural syntax, provides tools to introspect user-defined types and much more.

190 questions
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Taking n lines from a file which contains m lines, repeating the file (lazily) if necessary

I'm looking for a way to use a text file to generate as much text as I need by simply repeating the as few times as needed. In a purely functional language, like Haskell, the solution seems trivial: here I've posted the code for the review, and it…
Enlico
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boost::hana how to check if a type is std::optional?

I searched the boost::hana::traits I cannot find anything related to checking concept of types. For example is_vector, is_optional. Is there any tools in hana can simplify this? Moreover, I would like to branch the code based on the result thus it…
Wang
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Boost Hana Implement a custom Sequence

I'm facing a situation where I usually would create a custom class by inheriting from boost::hana::tuple. For example, by using the following code, template struct my_nonworking_custom_tuple_t : public boost::hana::tuple…
davidhigh
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Boost.Hana JSON example: Difference between string and decltype(std::to_string(...))

I just read the Boost.Hana tutorial but unfortunately got stuck very early. Could anybody explain to me why to_json for integers is implemented the way it is: template auto to_json(T const& x) -> decltype(std::to_string(x)) { return…
Nils
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Can a std::array be unpacked into a non-type template parameter pack with Boost.Hana?

template struct S {}; constexpr auto a = std::array{0, 1, 2}; I would like to unpack the elements of a as template arguments to S. That is; S<0, 1, 2>. A possible C++2a implementation: template typename…
invexed
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What is the use case of boost::hana forward declaration headers?

Most of the hana headers include also forward declaration headers contained in the subfolder fwd, e.g. #include
Adam Ryczkowski
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How the when<> trait in boost.Hana works?

I have some experience with std::enable_if. IIRC, it is about if a well-formed expression results in true return back the user type T (if given) or void via nested type alias. template struct enable_if; template
RaGa__M
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Convert from Boost Hana Tuple to Std Vector

I am trying to create a std::vector from a boost::hana::tuple at compile-time like so: boost::hana::tuple namesString{ "Hello", "World" }; std::vector namesStringVector{}; while(!(hana::is_empty(namesString))) { …
Ð..
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Define Hana struct with template parameters

Is there a way to define(adapt) a struct for Hana that has template parameters? The canonical example is a non-template class, #include #include namespace hana = boost::hana; struct Person { …
alfC
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using boost::hana for introspection

I'm walking through the examples of the help page of the awesome boost::hana library and am not able to get the introspection example working correctly. This code is intended to check at compile time whether an object has a specific member function…
Wum
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How to define get/set pair with BOOST_HANA_ADAPT_ADT?

I would like to introspect on an third-party ADT which defines pairs of getters/setters for access to "properties" of the class. For example: struct Echo { float mix; // read-only, don't ask why. void set_mix(float mix); }; I would like to…
seertaak
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Create a function signature from a hana tuple without the preprocessor

Is there a way to do this whitout the preprocessor? #include #include namespace ba = boost::hana; template struct FunctionSigCreatorImpl {}; template
chila
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hana types for template-of-templates

I am trying to generate a type that is using template-of-templates using boost::hana but ran into trouble. I have the following classes template typename BarModel> struct Foo { BarModel bar; } template
Hannes Ovrén
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Constexpr loop with a no constexpr content

I want to use boost hana to generate this final code: template < typename ... Ts > void foo(Ts ... data) { constexpr auto tuple = hana::make_tuple(data...); //Code that I need to be generate container_c[tuple[0_c]].foo2(); …
Mathieu Van Nevel
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How to remove metaprogramming recursion with Boost Hana

I'm trying to create a bitset according to the type send to the function. But let's reduce the test case a little. Warning : I'm using auto gcc extension for this example, I don't need to use template parameter. namespace hana =…
Mathieu Van Nevel
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