mirror of
https://github.com/triqs/dft_tools
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78 lines
2.0 KiB
ReStructuredText
78 lines
2.0 KiB
ReStructuredText
.. highlight:: c
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.. _util_tuple:
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Tuple compile time tools
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=============================
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Very useful for lib developers, they fill a missing gap in the std library.
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They implement various standard functional operations, at compile time,
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on tuple...
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.. note::
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Simple measures have shown that these routines are **as fast as native code** (tested on gcc, clang, icc),
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due to inlining. They can therefore be used in critical parts of codes.
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apply
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-----------------------------------------------
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*Purpose* : `apply a function on a tuple of arguments`
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Given a function object `f`, and its arguments stored in a tuple `t`, and we want to apply `f` on `t`.
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Python equivalent : `f(*t)`
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*Synopsis* ::
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template<typename Function, typename Tuple> auto apply (Function && f, Tuple const & t);
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*Solution* :
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.. compileblock::
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#include <triqs/utility/tuple_tools.hpp>
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#include <iostream>
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int main() {
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auto fun= [](int i, double x, double y, int k) {return 6*k + i - 1.3*x + 2*y;};
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auto t = std::make_tuple(1,2.3,4.3,8);
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auto res = triqs::tuple::apply(fun,t);
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std::cout << " f(t) =" << res << std::endl ;
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}
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for_each
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-------------------------------------------------------------------------
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*Purpose* : `apply a function for each element of a tuple (in order)`
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Given a function object `f`, we want to apply it to all elements of a tuple `t`.
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Python equivalent : `for x in t : f(x)`
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*Synopsis* ::
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template<typename Function, typename Tuple> void for_each(Tuple const & t, Function && f);
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*Solution* :
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.. compileblock::
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#include <triqs/utility/tuple_tools.hpp>
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#include <iostream>
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struct print_t { template<typename T> void operator()(T x) { std::cout << x << " "; } };
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int main() {
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auto t = std::make_tuple(1,2.3,4.3,8, "hello");
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triqs::tuple::for_each(t, print_t());
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// C++14 solution : with generic lambda, there is no need to define a print_t ...
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// triqs::tuple::for_each(t, [](auto x) { std::cout<<x<<" ";});
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}
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