mirror of
https://github.com/triqs/dft_tools
synced 2024-11-01 19:53:45 +01:00
115 lines
3.1 KiB
ReStructuredText
115 lines
3.1 KiB
ReStructuredText
.. highlight:: c
|
|
|
|
Automatic assignment
|
|
=======================
|
|
|
|
Principle
|
|
----------------
|
|
|
|
It is possible to use a subset of possible expressions as Left Hand Side (LHS) in an assignment statement, e.g. ::
|
|
|
|
A(x_) = some_expression_of_x_
|
|
A[i_] = some_expression_of_i_
|
|
A(x_)(i_,j_) = some_expression_of_x_i_j
|
|
A[x_](i_,j_) = some_expression_of_x_i_j
|
|
|
|
* Right Hand Side (RHS) of the = statement can be any expression.
|
|
* Left Hand Side (LHS) of the = sign. A must be a `lazy-assignable`, called by [] or (), one or several time.
|
|
|
|
This writing means that a regular function ::
|
|
|
|
x_ -> some_expression_of_x_
|
|
|
|
will be given to A so that it can fill itself by evaluating this function.
|
|
A determines the range of value of x on which the function is called.
|
|
|
|
Example
|
|
---------
|
|
|
|
.. compileblock::
|
|
|
|
#include "triqs/clef.hpp"
|
|
#include "triqs/clef/adapters/vector.hpp"
|
|
#include <iostream>
|
|
|
|
int main() {
|
|
int N = 10;
|
|
double pi = std::acos(-1);
|
|
std::vector<double> V(N);
|
|
|
|
// automatic assignment of vector and use of lazy math function
|
|
triqs::clef::placeholder <0> k_;
|
|
triqs::clef::lazy(V) [k_] << cos( (2* pi* k_)/ N );
|
|
|
|
// check result...
|
|
for (size_t u=0; u<V.size(); ++u) std::cout<< u << " "<<V[u]<< " "<< cos((2*pi*u)/N)<<std::endl;
|
|
}
|
|
|
|
Implementing automatic assign for an object
|
|
------------------------------------------------------------
|
|
|
|
It is sufficient to add a function ::
|
|
|
|
template<typename Fnt> void triqs_clef_auto_assign (Obj & x, Fnt f);
|
|
|
|
The compiler will rewrite ::
|
|
|
|
obj(x_,y_, ...) = expression
|
|
|
|
into ::
|
|
|
|
triqs_clef_auto_assign (obj, make_function( expression, x_, y_, ....))
|
|
|
|
The function is found by ADL. It is therefore useful to implement it e.g. as a friend function.
|
|
|
|
Similarly, for [ ], adding a function ::
|
|
|
|
template<typename Fnt> void triqs_clef_auto_assign_subscript (Obj & x, Fnt f);
|
|
|
|
The compiler will rewrite ::
|
|
|
|
obj[i_] = expression
|
|
|
|
into ::
|
|
|
|
triqs_clef_auto_assign_subscript (obj, make_function( expression, i_))
|
|
|
|
|
|
|
|
A complete example :
|
|
|
|
.. compileblock::
|
|
|
|
#include <triqs/clef.hpp>
|
|
#include <iostream>
|
|
|
|
struct Obj{
|
|
double v;
|
|
Obj(double v_): v(v_){}
|
|
|
|
// lazy call : cf ...
|
|
template< typename... Args>
|
|
typename triqs::clef::result_of::make_expr_call<std::reference_wrapper<const Obj>,Args...>::type
|
|
operator()( Args&&... args ) const { return make_expr_call (std::ref(* this),args...);}
|
|
|
|
// The non const version (which then stores a non-const reference ....)
|
|
template< typename... Args>
|
|
typename triqs::clef::result_of::make_expr_call<std::reference_wrapper<Obj>,Args...>::type
|
|
operator()( Args&&... args ) { return make_expr_call (std::ref(* this),args...);}
|
|
|
|
template<typename Fnt> friend void triqs_clef_auto_assign (Obj & x, Fnt f) {
|
|
x.v++; std::cout<< " called triqs_clef_auto_assign "<< f(100)<<std::endl;
|
|
}
|
|
friend std::ostream & triqs_clef_formal_print(std::ostream & out, Obj const & x) {return out<<"Obj";}
|
|
};
|
|
|
|
int main() {
|
|
Obj f(2);
|
|
triqs::clef::placeholder<3> x_;
|
|
std::cout<< f.v << std::endl;
|
|
f(x_ ) << 8*x_ ;
|
|
//f(x_ + y_) = 8*x_; // leads to a compile error as expected
|
|
std::cout<< f.v << std::endl;
|
|
}
|
|
|