TypeName.h

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/** @noop License Comment
 *  @file
 *  @copyright
 *  This Source Code is subject to the terms of the Mozilla Public License, v2.0.
 *  If a copy of the MPL was not distributed with this file You can obtain one at
 *  https://mozilla.org/MPL/2.0/
 *  
 *  @author David Mórász
 *  @date 2025
 */
 
/**
 * @file
 * @brief  Convert types to string
 */
 
#pragma once
 
#include <string>
#include "ConstexprXXH3.h"
 
#include "CoreMinimal.h"
#include "UnrealCtre.h"
#include "Mcro/TextMacros.h"
#include "Mcro/Platform.h"
#include "Mcro/Inheritance.h"
 
#define MCRO_EXPLICIT_TYPE_EXTRACTION defined(MCRO_EXPLICIT_PRETTY_FUNCTION) && defined(MCRO_EXPLICIT_TYPE_EXTRACT_REGEX)
 
// TODO: C++ 20's std::source_location was used instead of this bouquet of macros, but then some platforms don't have <source_location>
#if MCRO_COMPILER_GCC || MCRO_COMPILER_CLANG
#define PRETTY_FUNC __PRETTY_FUNCTION__
#elif MCRO_COMPILER_MSVC
#define PRETTY_FUNC __FUNCSIG__
#elif MCRO_EXPLICIT_TYPE_EXTRACTION
#define PRETTY_FUNC MCRO_EXPLICIT_PRETTY_FUNCTION
#else
#error "TTypeName is only compatible with Clang, GCC and MSVC. Please create a PR for your compiler at https://github.com/microdee/mcro/pulls.
#error "If your compiler is under NDA add the following definitions in your target rules (values are examples):"
#error "`MCRO_EXPLICIT_PRETTY_FUNCTION=__PRETTY_FUNCTION__`"
#error "`MCRO_EXPLICIT_TYPE_EXTRACT_REGEX=\"GetCompileTimeTypeName\\\\<((struct|class)\\\\s)?(?<TYPE>.+?)\\\\>\\\\(\"`"
#endif
 
// disable this warning to allow us exploit division by zero error in consteval
#pragma warning(push)
#pragma warning(disable: 4804) // unsafe use of type 'bool' in operation
 
/**
 *  @brief  Get a string view of the compile time typename
 *  
 *  @note
 *  Using std::(w)string here instead of FString or FStringView for consteval compatibility
 *  
 *  @tparam  T  target type
 *  @return  string view of the name of the type
 */
template <typename T>
consteval std::basic_string_view<TCHAR> GetCompileTimeTypeName()
{
    using namespace Mcro::Text;
    std::basic_string_view<TCHAR> thisFunctionName { TEXT(PRETTY_FUNC) };
    
#if MCRO_COMPILER_GCC || MCRO_COMPILER_CLANG
    
    // on Clang thisFunctionName looks like this:
    //        matching: [--------------------------------------------]
    //                  |                  capturing: [-------------]|
    // std::string_view GetCompileTimeTypeName() [T = MyTemplate<Vec>]
    
    // on GCC thisFunctionName has a similar enough format so we can use the same pattern:
    //                  matching: [-------------------------------------------------]
    //                            |                       capturing: [-------------]|
    // consteval std::string_view GetCompileTimeTypeName() [with T = MyTemplate<Vec>; std::string_view = std::basic_string_view<char>]
    
    auto result = ctre::search<TEXT_ R"(\s\[(?:with\s)?T\s=\s(?<TYPE>.+?)[;\]])">(thisFunctionName);
    
#elif MCRO_COMPILER_MSVC
    
    // on MSVC thisFunctionName looks like this:
    //                                                                 matching: [----------------------------------------------------]
    //                                                                           |                  capturing: [---------------------]|
    // class std::basic_string_view<char,struct std::char_traits<char> > __cdecl GetCompileTimeTypeName<struct MyTemplate<struct Vec>>(void)
    
    auto result = ctre::search<TEXT_ R"(GetCompileTimeTypeName<((struct|class)\s)?(?<TYPE>.+?)>\‍()">(thisFunctionName);
 
#elif MCRO_EXPLICIT_TYPE_EXTRACTION
    auto result = ctre::search<TEXT(MCRO_EXPLICIT_TYPE_EXTRACT_REGEX)>(thisFunctionName);
#endif
    
    std::basic_string_view<TCHAR> output = result.get<TEXT_"TYPE">().to_view();
    size_t size = output.size();
    size /= output.size() > 0; // Fail compilation with division-by-zero if we couldn't extract a typename
    
    return size ? output : std::basic_string_view<TCHAR>();
}
 
/** Convert types to string */
namespace Mcro::TypeName
{
    using namespace Mcro::Text;
    using namespace Mcro::Inheritance;
 
    using FTypeHash = uint64;
 
    template <typename T>
    consteval FTypeHash GetCompileTimeTypeHash()
    {
        std::string_view thisFunctionName { PRETTY_FUNC };
        return constexpr_xxh3::XXH3_64bits_const(thisFunctionName);
    }
    
    /**
     *  @brief
     *  Get a friendly string of an input type without using `typeid(T).name()`.
     *
     *  Actually this method gives more predictable results across compilers than `typeid(T).name()` but still not 100%
     *  the same. Besides TTypeName can deal with incomplete types as well, whereas `typeid(T)` cannot (more on this in
     *  remarks). While it is more consistent across compilers, it is still not 100% consistent. Take templated types
     *  for instance where MSVC compiler will add "class" prefix in front of type arguments where GCC or CLang might not.
     *  Because of subtle differences like this, it is strongly discouraged to assume the exact format of the output of
     *  TTypeName
     *  
     *  Usage:
     *  @code
     *  FStringView myTypeName = TTypeName<FMyType>;
     *  @endcode
     *  
     *  It is useful in templates where a type name should be known in runtime as well. (e.g.: Modular features)
     *  
     *  @remarks
     *  Note on incomplete types: incomplete types on MSVC are localized to current scope. which means
     *  @code
     *  class I;
     *  
     *  class A
     *  {
     *      FStringView GetName() { return TTypeName<I>; }
     *      // Returns "I"
     *  }
     *  @endcode
     *  BUT:
     *  @code
     *  class A
     *  {
     *      FStringView GetName() { return TTypeName<class I>; }
     *      // Returns "A::GetName::I"
     *  }
     *  @endcode
     *  as you can see they are not equal. For sake of simplicity TTypeName only supports incomplete
     *  types when they're declared in global scope. Any other case might yield undesired results
     *  (e.g.: `TTypeName<class I>` of incomplete `I` might not be the same as `TTypeName<I>` somewhere
     *  else with `I` being fully defined)
     *  
     *  @tparam  T  The type to be named
     *
     *  @warning
     *  Do not use exact type comparison with serialized data or network communication, as the actual value of the type
     *  is different between compilers. Only use this for runtime data. For such scenarios just use Unreal's own UObjects.
     */
    template <typename T>
    constexpr FStringView TTypeName = FStringView(
        GetCompileTimeTypeName<std::decay_t<T>>().data(),
        GetCompileTimeTypeName<std::decay_t<T>>().size()
    );
 
    /** @brief Same as `TTypeName` just stored as STL string made during compile time */
    template <typename T>
    constexpr std::basic_string_view<TCHAR> TTypeNameStd = GetCompileTimeTypeName<std::decay_t<T>>();
 
    /** @brief Get a fixed `uint64` hash representation of the given type. Have similar caveats as `TTypeName` */
    template <typename T>
    constexpr FTypeHash TTypeHash = GetCompileTimeTypeHash<T>();
 
    /**
     *  @brief
     *  Same as `TTypeName` converted to FName. This is not cached and a new FName is created every time this is called.
     */
    template <typename T>
    FName TTypeFName()
    {
        return FName(TTypeName<T>.Len(), TTypeName<T>.GetData());
    }
 
    /**
     *  @brief
     *  Same as `TTypeName` converted to FString. This is not cached and a new FString is created every time this is called.
     */
    template <typename T>
    FString TTypeString()
    {
#if UE_VERSION_OLDER_THAN(5, 5, 0)
        return FString(TTypeName<T>.Len(), TTypeName<T>.GetData());
#else
        return FString::ConstructFromPtrSize(TTypeName<T>.GetData(), TTypeName<T>.Len());
#endif
    }
}
 
#pragma warning(pop)