UnrealTypeTraits.h

#pragma once

#include "IsEnum.h"
#include "IsPointer.h"
#include "IsArithmetic.h"
#include "AndOrNot.h"
#include "IsPODType.h"
#include "IsTriviallyCopyConstructible.h"

template <typename T, bool TypeIsSmall>
struct TCallTraitsParamTypeHelper
{
	typedef const T& ParamType;
	typedef const T& ConstParamType;
};
template <typename T>
struct TCallTraitsParamTypeHelper<T, true>
{
	typedef const T ParamType;
	typedef const T ConstParamType;
};
template <typename T>
struct TCallTraitsParamTypeHelper<T*, true>
{
	typedef T* ParamType;
	typedef const T* ConstParamType;
};

template <typename T>
struct TCallTraitsBase
{
private:
	enum { PassByValue = TOr<TAndValue<(sizeof(T) <= sizeof(void*)), TIsPODType<T>>, TIsArithmetic<T>, TIsPointer<T>>::Value };
public:
	typedef T ValueType;
	typedef T& Reference;
	typedef const T& ConstReference;
	typedef typename TCallTraitsParamTypeHelper<T, PassByValue>::ParamType ParamType;
	typedef typename TCallTraitsParamTypeHelper<T, PassByValue>::ConstParamType ConstPointerType;
};

/**
 * TCallTraits
 */
template <typename T>
struct TCallTraits : public TCallTraitsBase<T> {};

// Fix reference-to-reference problems.
template <typename T>
struct TCallTraits<T&>
{
	typedef T& ValueType;
	typedef T& Reference;
	typedef const T& ConstReference;
	typedef T& ParamType;
	typedef T& ConstPointerType;
};

// Array types
template <typename T, size_t N>
struct TCallTraits<T[N]>
{
private:
	typedef T ArrayType[N];
public:
	typedef const T* ValueType;
	typedef ArrayType& Reference;
	typedef const ArrayType& ConstReference;
	typedef const T* const ParamType;
	typedef const T* const ConstPointerType;
};

// const array types
template <typename T, size_t N>
struct TCallTraits<const T[N]>
{
private:
	typedef const T ArrayType[N];
public:
	typedef const T* ValueType;
	typedef ArrayType& Reference;
	typedef const ArrayType& ConstReference;
	typedef const T* const ParamType;
	typedef const T* const ConstPointerType;
};


/*-----------------------------------------------------------------------------
	Traits for our particular container classes
-----------------------------------------------------------------------------*/

/**
 * Helper for array traits. Provides a common base to more easily refine a portion of the traits
 * when specializing. Mainly used by MemoryOps.h which is used by the contiguous storage containers like TArray.
 */
template<typename T>
struct TTypeTraitsBase
{
	typedef typename TCallTraits<T>::ParamType ConstInitType;
	typedef typename TCallTraits<T>::ConstPointerType ConstPointerType;

	// There's no good way of detecting this so we'll just assume it to be true for certain known types and expect
	// users to customize it for their custom types.
	enum { IsBytewiseComparable = TOr<TIsEnum<T>, TIsArithmetic<T>, TIsPointer<T>>::Value };
};

/**
 * Traits for types.
 */
template<typename T> struct TTypeTraits : public TTypeTraitsBase<T> {};

template <typename T, typename Arg>
struct TIsBitwiseConstructible
{
	// Assume no bitwise construction in general
	enum { Value = false };
};

template <typename T>
struct TIsBitwiseConstructible<T, T>
{
	// Ts can always be bitwise constructed from itself if it is trivially copyable.
	enum { Value = TIsTriviallyCopyConstructible<T>::Value };
};

template <typename T, typename U>
struct TIsBitwiseConstructible<const T, U> : TIsBitwiseConstructible<T, U>
{
	// Constructing a const T is the same as constructing a T
};

// Const pointers can be bitwise constructed from non-const pointers.
// This is not true for pointer conversions in general, e.g. where an offset may need to be applied in the case
// of multiple inheritance, but there is no way of detecting that at compile-time.
template <typename T>
struct TIsBitwiseConstructible<const T*, T*>
{
	// Constructing a const T is the same as constructing a T
	enum { Value = true };
};

// Unsigned types can be bitwise converted to their signed equivalents, and vice versa.
// (assuming two's-complement, which we are)
template <> struct TIsBitwiseConstructible<uint8, char> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible< char, uint8> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible<uint16, short> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible< short, uint16> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible<uint32, int32> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible< int32, uint32> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible<uint64, int64> { enum { Value = true }; };
template <> struct TIsBitwiseConstructible< int64, uint64> { enum { Value = true }; };