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predicate.hpp

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#pragma once

#include <cstddef>

#include "cexpr/string.hpp"

namespace sql

{

namespace

{

// shim to allow all value types like double or float to be used as non-type template parameters.

template <typename Type>

struct value

{

constexpr value(Type v) : val{ v }

{}

Type val;

};

} // namespace

template <cexpr::string Op, typename Row, typename Left, typename Right=void>

struct operation

{

static constexpr bool eval(Row const& row) noexcept

{

if constexpr (Op == "=")

{

return Left::eval(row) == Right::eval(row);

}

else if constexpr (Op == ">")

{

return Left::eval(row) > Right::eval(row);

}

else if constexpr(Op == "<")

{

return Left::eval(row) < Right::eval(row);

}

else if constexpr(Op == ">=")

{

return Left::eval(row) >= Right::eval(row);

}

else if constexpr(Op == "<=")

{

return Left::eval(row) <= Right::eval(row);

}

else if constexpr(Op == "!=" || Op == "<>")

{

return Left::eval(row) != Right::eval(row);

}

else if constexpr(Op == "AND")

{

return Left::eval(row) && Right::eval(row);

}

else if constexpr(Op == "OR")

{

return Left::eval(row) || Right::eval(row);

}

else if constexpr(Op == "NOT")

{

return !Left::eval(row);

}

}

};

template <cexpr::string Column, typename Row>

struct variable

{

static constexpr auto eval(Row const& row) noexcept

{

return sql::get<Column>(row);

}

};

template <auto Const, typename Row>

struct constant

{

static constexpr auto eval([[maybe_unused]] Row const& row) noexcept

{

return Const.val;

}

};

} // namespace sql