80 lines
2.2 KiB
C++
80 lines
2.2 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include <fmt/core.h>
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#include <utility>
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#include <iosfwd>
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#include <string>
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namespace cruft {
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/// A base exception class for all cruft libraries.
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///
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/// There is deliberately no `what` method as it's not always acceptable
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/// to store a string that we can return a pointer to. Instead we rely on
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/// the `describe` method to output to a std::ostream. The user can wrangle
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/// that into a std::string if they need one.
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class error {
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public:
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virtual ~error () = default;
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virtual std::ostream& describe (std::ostream&) const = 0;
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};
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/// A mixin error class that can be used when inheriting from
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/// `cruft::error`.
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///
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/// It accepts a single std::string, saving it so that it can be passed
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/// through to a std::ostream later on.
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///
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/// By setting `BaseT` to a locally useful error class we can still
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/// maintain an appropriate exception hierarchy for a given module.
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/// eg, pass `foo::error` (which derives eventually from `cruft::error`)
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/// in the module `foo`.
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///
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/// \tparam BaseT The desired base class.
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template <typename BaseT>
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class string_error : public BaseT {
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public:
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template <typename... Args>
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string_error (std::string const &_message, Args &&...args)
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: BaseT (std::forward<Args> (args)...)
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, m_message (_message)
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{ ; }
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std::ostream&
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describe (std::ostream &os) const override
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{
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return os << m_message;
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}
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private:
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std::string m_message;
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};
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/// Use `error::describe` to render the supplied error object to a
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/// std::ostream.
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std::ostream&
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operator<< (std::ostream &os, error const&);
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}
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template <>
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struct fmt::formatter<cruft::error> {
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constexpr format_parse_context::iterator
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parse (format_parse_context &ctx)
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{
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return ctx.begin ();
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}
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format_context::iterator
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format (cruft::error const&, format_context &ctx);
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}; |