gui_result.h

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#pragma once
 
#include <string>
#include <utility>
#include <variant>
 
namespace tachyon
{

    enum class ErrorCode : uint8_t
    {
        Failed,          
        InvalidArgument,
        NotFound,        
        ParseFailed,     
        Unsupported,     
        OutOfMemory,
        DeviceLost,      
    };

    struct Error
    {
        ErrorCode   code = ErrorCode::Failed;
        std::string message;    
    };

    template<class T>
    class [[nodiscard]] Result
    {
    public:
        Result(T value) : m_value(std::move(value)) {}
        Result(Error error) : m_value(std::move(error)) {}

        bool     HasValue() const          { return m_value.index() == 0; }
        explicit operator bool() const     { return HasValue(); }

        T&       Value()                   { return std::get<0>(m_value); }
        const T& Value() const             { return std::get<0>(m_value); }
        T&       operator*()               { return Value(); }
        const T& operator*() const         { return Value(); }
        T*       operator->()              { return &Value(); }
        const T* operator->() const        { return &Value(); }
        T        ValueOr(T fallback) const { return HasValue() ? Value() : std::move(fallback); }

        const Error& GetError() const      { return std::get<1>(m_value); }
 
    private:
        std::variant<T, Error> m_value;
    };

    template<>
    class [[nodiscard]] Result<void>
    {
    public:
        Result() = default;
        Result(Error error) : m_error(std::move(error)), m_failed(true) {}

        bool     HasValue() const      { return !m_failed; }
        explicit operator bool() const { return HasValue(); }

        const Error& GetError() const  { return m_error; }
 
    private:
        Error m_error {};
        bool  m_failed = false;
    };

}