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@philsquared
Created April 11, 2013 23:45
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How to write the "left arrow operator" to enable extension methods in C++
#include <cassert>
#include <iostream>
template<typename T, typename R=void>
struct ExtMethod {
ExtMethod& operator - () {
return *this;
}
template<typename U>
R operator()( U& obj ) {
return static_cast<T*>(this)->operator()( obj );
}
};
template<typename Derived>
struct Extendible
{
template<typename T, typename ReturnT>
ReturnT operator < ( ExtMethod<T, ReturnT>& extMethod ) {
return extMethod( static_cast<Derived&>( *this ) );
}
};
struct Widget : Extendible<Widget> {
Widget( int size, int weight ) : size( size ), weight( weight ) {}
int size;
int weight;
};
struct print : ExtMethod<print> {
void operator()( Widget& w ) {
std::cout << "size: " << w.size << ", weight: " << w.weight << std::endl;
}
};
struct density : ExtMethod<density, float> {
float operator()( Widget& w ) {
return (float)(w.weight / w.size);
}
};
int main() {
Widget w( 4, 10 );
w<-print();
float d = w<-density();
assert( d - 10/4 < 0.01 );
}
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