mirror of
https://github.com/triqs/dft_tools
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3fd3f38446
- was not compiling on gcc (forward declaration issue). - now clearer - add a trivial print change in the mc class (to avoid trivial commit).
131 lines
4.3 KiB
ReStructuredText
131 lines
4.3 KiB
ReStructuredText
.. highlight:: c
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Overloading functions and methods for CLEF arguments
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=====================================================
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.. _overload_function:
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Overloading functions
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----------------------------
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Given a function, it is possible to overload it for CLEF expression arguments, returning a CLEF expression
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using the `TRIQS_CLEF_MAKE_FNT_LAZY` macro.
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**Synopsis** ::
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namespace triqs { namespace clef {
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TRIQS_CLEF_MAKE_FNT_LAZY (function_to_make_lazy);
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}}
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For example:
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.. compileblock::
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#include <triqs/clef.hpp>
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#include <iostream>
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// a simple foo function
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double foo(double x) { return x/2;}
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int foo(int x) { return x*2;}
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// a more complex case : bar is already a template
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// we have to disable it for CLEF expression to avoid ambiguity
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// C++14 clean syntax will be (using concepts)
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// template<NotClefExpression T>
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// T bar (T const & x) { return x+1;}
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// C++11 workaround
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template<typename T>
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typename std::enable_if<!triqs::clef::is_clef_expression<T>::value,T>::type
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bar (T const & x) { return x+1;}
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namespace triqs { namespace clef { TRIQS_CLEF_MAKE_FNT_LAZY (foo) ; TRIQS_CLEF_MAKE_FNT_LAZY (bar) ; }}
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int main() {
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triqs::clef::placeholder<3> x_;
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std::cout << foo(2.0)<<" "<<eval(x_ + foo(x_), x_ = 3)<<" "<<eval(x_ + foo(x_), x_ = 3.5) << std::endl;
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std::cout << bar(2.0)<<" "<<eval(x_ + bar(x_), x_ = 3)<<" "<<eval(x_ + bar(x_), x_ = 3.5) << std::endl;
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}
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Note that :
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* This overload **must** be defined in the triqs::clef namespace, since it is found by ADL.
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* The function `foo` can have many overloads.
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* The function `bar` can be a template, BUT then the template must be disabled for lazy expressions.
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* The overload is already defined by clef for usual functions :
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.. compileblock::
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#include <triqs/clef.hpp>
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#include <iostream>
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int main() {
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triqs::clef::placeholder<3> x_;
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std::cout << 2.0 + std::cos(2.0) << std::endl;
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std::cout << eval( x_ + cos(x_), x_ = 2) << std::endl; // NB : note the absence of std::
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}
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.. _callable_object:
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Overloading operator() and other methods
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---------------------------------------------------
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Similarly to functions, classes can define an `operator()` for CLEF expressions arguments (or any other method).
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It is an ordinary operator() that must :
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* Be enabled only when one argument is a CLEF expression
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* Return a CLEF expression.
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Example :
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.. compileblock::
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#include <triqs/clef.hpp>
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struct Obj {
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double v; // put something in it
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Obj(double v_): v(v_){} // constructor
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Obj(Obj const &) = delete; // a non copyable object, to illustrate that we do NOT copy...
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// The "normal", non CLEF call operator ....
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double operator() (double x) const { return 10*x;}
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// This macro implements properly an overload of the operator ()
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TRIQS_CLEF_IMPLEMENT_LAZY_CALL();
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// a method
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double my_method(double x) const { return 2*x;}
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// CLEF overload
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// WARNING : the method MUST be const
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TRIQS_CLEF_IMPLEMENT_LAZY_METHOD(Obj,my_method);
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// Just to print itself nicely in the expressions
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friend std::ostream & operator<<(std::ostream & out, Obj const & x) { return out<<"Obj";}
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};
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int main() {
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Obj f(7);
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triqs::clef::placeholder<1> x_; triqs::clef::placeholder<2> y_;
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std::cout << "Clef expression : "<< f(y_) + 2*x_ << std::endl ;
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std::cout << "Complete evaluation : "<< eval(f(x_) + 2*x_, x_=1) << std::endl ;
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std::cout << "Partial evaluation : "<< eval(f(y_) + 2*x_, y_=1) << std::endl ;
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std::cout << "Complete evalution : "<< eval(f(y_) + 2*x_, x_=3, y_=1) << std::endl<<std::endl ;
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std::cout << "Clef expression : "<< f.my_method(y_) + 2*x_ << std::endl ;
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std::cout << "Complete evaluation : "<< eval(f.my_method(x_) + 2*x_, x_=1) << std::endl ;
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std::cout << "Partial evaluation : "<< eval(f.my_method(y_) + 2*x_, y_=1) << std::endl ;
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std::cout << "Complete evalution : "<< eval(f.my_method(y_) + 2*x_, x_=3, y_=1) << std::endl ;
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}
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**NB** When the method or the non CLEF operator() is already a template,
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it must be disabled for clef expression argument, using the trait ::
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clef::is_clef_expression<T...> // true iif one of the T is a clef expression
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as the `bar` function above.
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