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Introduce ngt::AnyBuffer #49235

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5 changes: 5 additions & 0 deletions HeterogeneousCore/SerialisationCore/README.md
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# `ngt::AnyBuffer`

`ngt::AnyBuffer` behaves like `std::any`, with two differences: it can only be
used with trivially copyable types, and provides access to the underlying memory
buffer to allow `memcpy`'ing its content.
74 changes: 74 additions & 0 deletions HeterogeneousCore/SerialisationCore/interface/AnyBuffer.h
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#ifndef HeterogeneousCore_SerialisationCore_interface_AnyBuffer_h
#define HeterogeneousCore_SerialisationCore_interface_AnyBuffer_h

#include <type_traits>
#include <typeinfo>
#include <cstddef>

#include <boost/container/small_vector.hpp>

#include "FWCore/Utilities/interface/EDMException.h"
#include "FWCore/Utilities/interface/TypeDemangler.h"

namespace ngt {

class AnyBuffer {
public:
AnyBuffer() = default;

template <typename T>
AnyBuffer(T const& t)
requires(std::is_trivially_copyable_v<T>)
: storage_(reinterpret_cast<std::byte const*>(&t), reinterpret_cast<std::byte const*>(&t) + sizeof(T)),
typeid_(&typeid(std::remove_cv_t<T>)) {}

template <typename T>
T& cast_to()
requires(std::is_trivially_copyable_v<T>)
{
if (empty()) {
throw edm::Exception(edm::errors::LogicError)
<< "Attempt to read an object of type " << edm::typeDemangle(typeid(T).name())
<< " from an empty AnyBuffer";
}
if (typeid(std::remove_cv_t<T>) != *typeid_) {
throw edm::Exception(edm::errors::LogicError)
<< "Attempt to read an object of type " << edm::typeDemangle(typeid(T).name())
<< " from an AnyBuffer holding an object of type " << edm::typeDemangle(typeid_->name());
}
return *reinterpret_cast<T*>(storage_.data());
}

template <typename T>
T const& cast_to() const
requires(std::is_trivially_copyable_v<T>)
{
if (empty()) {
throw edm::Exception(edm::errors::LogicError)
<< "Attempt to read an object of type " << edm::typeDemangle(typeid(T).name())
<< " from an empty AnyBuffer";
}
if (typeid(std::remove_cv_t<T>) != *typeid_) {
throw edm::Exception(edm::errors::LogicError)
<< "Attempt to read an object of type " << edm::typeDemangle(typeid(T).name())
<< " from an AnyBuffer holding an object of type " << edm::typeDemangle(typeid_->name());
}
return *reinterpret_cast<T const*>(storage_.data());
}

bool empty() const { return typeid_ == nullptr; }

std::byte* data() { return storage_.data(); }

std::byte const* data() const { return storage_.data(); }

size_t size_bytes() const { return storage_.size(); }

private:
boost::container::small_vector<std::byte, 32> storage_; // small_vector size chosen to fit AnyBuffer in 64 bytes
std::type_info const* typeid_ = nullptr;
};

} // namespace ngt

#endif // HeterogeneousCore_SerialisationCore_interface_AnyBuffer_h