schema_editor/comdel/parser/presult.h

#ifndef PRESULT_H
#define PRESULT_H

#include "expected.h"
#include "source_error.h"

#include <optional>

/// Returns from the CURRENT function, the one this macro is used in,
/// if PResult contains an error
#define RETURN_IF_ERR(presult) \
    do { \
        auto&& return_if_err_temp_ = (presult); \
        if (!return_if_err_temp_) { \
            return PError(return_if_err_temp_.error()); \
        } \
    } while (0)

/// Works the same as RETURN_IF_ERR but can also assign the unwrapped result
/// to a variable if successful
#define ASSIGN_OR_RETURN_IF_ERR(var, presult) \
    do { \
        auto&& assign_or_return_if_err_temp_ = (presult); \
        if (!assign_or_return_if_err_temp_) { \
            return PError(assign_or_return_if_err_temp_.error()); \
        } else { \
            var = *assign_or_return_if_err_temp_; \
        } \
    } while (0)

using PError = tl::unexpected<SourceError>;

/// Holds either an AST node or an error
/// The value MUST be checked before usage, e.g. using RETURN_IF_ERR
template<typename T>
struct PResult : tl::expected<T, SourceError> {
    using tl::expected<T, SourceError>::expected;

    /// Implicit conversion from PResult<U> to PResult<T>
    /// if U is convertible to T
    template<typename U, class V = std::enable_if_t<std::is_convertible<std::decay_t<U>, T>::value>>
    PResult(PResult<U> presult) :
            tl::expected<T, SourceError>(presult ? PResult<T>(*presult) : PError(presult.error())) {}
};

/// Alternative to PResult that is returned from parseLibrary* functions
/// that only consume one token so they can fail without affecting
/// the parser state
template<typename T>
struct POptResult : public PResult<T> {
    using PResult<T>::PResult;

    std::optional<T> optional() {
        if (*this) {
            return **this;
        } else {
            return std::nullopt;
        }
    }
};


#endif // PRESULT_H