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#pragma once
#include <Core/Field.h>
namespace DB
{
/** StaticVisitor (and its descendants) - class with overloaded operator() for all types of fields.
* You could call visitor for field using function 'applyVisitor'.
* Also "binary visitor" is supported - its operator() takes two arguments.
*/
template <typename R = void>
struct StaticVisitor
{
using ResultType = R;
};
/// F is template parameter, to allow universal reference for field, that is useful for const and non-const values.
template <typename Visitor, typename F>
auto applyVisitor(Visitor && visitor, F && field)
{
return Field::dispatch(std::forward<Visitor>(visitor),
std::forward<F>(field));
}
template <typename Visitor, typename F1, typename F2>
auto applyVisitor(Visitor && visitor, F1 && field1, F2 && field2)
{
return Field::dispatch(
[&field2, &visitor](auto & field1_value)
{
return Field::dispatch(
[&field1_value, &visitor](auto & field2_value)
{
return visitor(field1_value, field2_value);
},
std::forward<F2>(field2));
},
std::forward<F1>(field1));
}
}
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