Conditionals.h

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// Copyright Epic Games, Inc. All Rights Reserved.
// Templates for conditional flow control inside other templates
 
#pragma once
 
namespace uLang
{
 
//------------------------------------------------------------------
// From AndOrNot.h
 
template <typename... Types>
struct TAnd;
 
template <bool LHSValue, typename... RHS>
struct TAndValue
{
    enum { Value = TAnd<RHS...>::Value };
};
 
template <typename... RHS>
struct TAndValue<false, RHS...>
{
    enum { Value = false };
};
 
template <typename LHS, typename... RHS>
struct TAnd<LHS, RHS...> : TAndValue<LHS::Value, RHS...>
{
};
 
template <>
struct TAnd<>
{
    enum { Value = true };
};
 
template <typename... Types>
struct TOr;
 
template <bool LHSValue, typename... RHS>
struct TOrValue
{
    enum { Value = TOr<RHS...>::Value };
};
 
template <typename... RHS>
struct TOrValue<true, RHS...>
{
    enum { Value = true };
};
 
template <typename LHS, typename... RHS>
struct TOr<LHS, RHS...> : TOrValue<LHS::Value, RHS...>
{
};
 
template <>
struct TOr<>
{
    enum { Value = false };
};
 
template <typename Type>
struct TNot
{
    enum { Value = !Type::Value };
};
 
//------------------------------------------------------------------
// From EnableIf.h
 
template <bool Predicate, typename Result = void>
class TEnableIf;
 
template <typename Result>
class TEnableIf<true, Result>
{
public:
    using Type = Result;
};
 
template <typename Result>
class TEnableIf<false, Result>
{};
 
template <bool Predicate, typename Result = void>
using TEnableIfT = typename TEnableIf<Predicate, Result>::Type;
 
//------------------------------------------------------------------
// From ChooseClass.h
 
template<bool Predicate, typename TrueClass, typename FalseClass>
class TChooseClass;
 
template<typename TrueClass, typename FalseClass>
class TChooseClass<true, TrueClass, FalseClass>
{
public:
    using Result = TrueClass;
};
 
template<typename TrueClass, typename FalseClass>
class TChooseClass<false, TrueClass, FalseClass>
{
public:
    using Result = FalseClass;
};
 
}