63 lines
1.6 KiB
C++
63 lines
1.6 KiB
C++
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#pragma once
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#include <vector>
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namespace europa::util {
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template <class To, class From>
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struct IntoImpl {
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constexpr static To DoInto(const From& from) {
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// The default implentation assumes that the To type has a constructor which
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// can initalize it from a value of From const&.
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return To(from);
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}
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};
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/// Into() support for vectors of items.
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template <class To, class From>
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struct IntoImpl<std::vector<To>, std::vector<From>> {
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constexpr static std::vector<To> DoInto(const std::vector<From>& from) {
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// FIXME: Ranges could make this less stupid
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auto vec = std::vector<To> {};
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vec.resize(from.size());
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// Feed into existing Into() implementation
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for(auto const& item : from)
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vec.push_back(Into(item));
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return vec;
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}
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};
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/// Allows a type to be converted.
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/// A user is allowed to supply conversions out-of-band.
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template <class To, class From>
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constexpr To Into(const From& from) {
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return IntoImpl<To, From>::DoInto(from);
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}
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/// Helper macro to hide away the annoying boilerplate of
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/// implementing the IntoImpl struct used for implementing conversion
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#define EUROPA_BEGIN_INTO_CONVERSION(To, From) \
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template <> \
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struct ::europa::util::IntoImpl<To, From> { \
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static To DoInto([[maybe_unused]] const From& from)
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#define EUROPA_END_INTO_CONVERSION }
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#if 0
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// An example of specializing Into().
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// This is a bit iffy, but works.
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struct Frob {};
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EUROPA_BEGIN_INTO_CONVERSION(int, Frob) {
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return 42;
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} EUROPA_END_INTO_CONVERSION;
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auto a() {
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Frob f{};
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int i = Into<int>(f);
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}
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#endif
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} // namespace europa::util
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