Ichthyostega
99c478768c
...based on all the clean-up and reorganisation done thus far, we're now able to rebuild the util::str in a more direct and sane way, and thus to disentangle the header inclusion problem.
299 lines
8.6 KiB
C++
299 lines
8.6 KiB
C++
/*
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UTIL.hpp - metaprogramming helpers and utilities
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Copyright (C) Lumiera.org
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2008, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/** @file util.hpp
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** Simple and lightweight helpers for metaprogramming and type detection.
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** This header is a collection of very basic type detection and metaprogramming utilities.
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** @warning indirectly, this header gets included into the majority of compilation units.
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** Avoid anything here which increases compilation times or adds much debugging info.
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**
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** @see MetaUtils_test
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** @see trait.hpp
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** @see typelist.hpp
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**
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*/
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#ifndef LIB_META_UTIL_H
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#define LIB_META_UTIL_H
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#include <typeinfo>
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namespace std { // forward declaration for std::string...
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template<typename C>
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struct char_traits;
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template<typename T>
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class allocator;
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template<typename c, class TRAIT, class _ALLO>
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class basic_string;
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using string = basic_string<char, char_traits<char>, allocator<char>>;
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}
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namespace lib {
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class Literal;
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class Symbol;
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namespace meta {
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/* === conditional definition selector === */
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template <bool B, class T = void>
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struct enable_if_c {
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typedef T type;
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};
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template <class T>
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struct enable_if_c<false, T> {};
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/** SFINAE helper to control the visibility of specialisations and overloads.
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* \par explanation
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* This template needs to be interspersed somehow into a type expression, which
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* is driven by an external, primary type parameter. Thus, it is possible to use
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* it on an extraneous, possibly default template parameter, or when forming the
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* return type of a function. The purpose is to remove a given definition from
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* sight, unless a boolean condition `Cond::value` holds true. In the typical
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* usage, this condition is suppled by a _metafunction_, i.e. a template, which
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* detects some feature or other circumstantial condition with the types involved.
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* @remarks this is a widely used facility, available both from boost and from
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* the standard library. For the most common case, we roll our own
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* variant here, which is slightly stripped down and a tiny bit
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* more concise than the boost variant. This way, we can avoid
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* a lot of boost inclusions, which always bear some weight.
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* @see [std::enable_if](http://en.cppreference.com/w/cpp/types/enable_if)
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*/
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template <class Cond, class T = void>
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using enable_if = typename enable_if_c<Cond::value, T>::type;
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template <class Cond, class T = void>
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using disable_if = typename enable_if_c<not Cond::value, T>::type;
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/* === building metafunctions === */
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/** helper types to detect the overload resolution chosen by the compiler */
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typedef char Yes_t;
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struct No_t { char more_than_one[4]; };
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/** detect possibility of a conversion to string.
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* Naive implementation just trying the direct conversion.
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* The embedded constant #value will be true in case this succeeds.
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* Might fail in more tricky situations (references, const, volatile)
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* @see \ref format-obj.hpp more elaborate solution including lexical_cast
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*/
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template<typename X>
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struct can_convertToString
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{
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static X & probe();
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static Yes_t check(std::string);
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static No_t check(...);
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public:
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static const bool value = (sizeof(Yes_t)==sizeof(check(probe())));
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};
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/** toggle for explicit specialisations */
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template<typename X>
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using enable_CustomStringConversion = enable_if<can_convertToString<X>>;
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/** strip const from type: naive implementation */
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template<typename T>
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struct UnConst
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{
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typedef T Type;
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};
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template<typename T>
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struct UnConst<const T>
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{
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typedef T Type;
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};
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template<typename T>
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struct UnConst<const T *>
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{
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typedef T* Type;
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};
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template<typename T>
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struct UnConst<T * const>
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{
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typedef T* Type;
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};
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template<typename T>
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struct UnConst<const T * const>
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{
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typedef T* Type;
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};
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/** Trait template for detecting a typelist type.
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* For example, this allows to write specialisations with the help of
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* boost::enable_if
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*/
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template<typename TY>
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class is_Typelist
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{
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template<class X>
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static Yes_t check(typename X::List *);
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template<class>
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static No_t check(...);
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public:
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static const bool value = (sizeof(Yes_t)==sizeof(check<TY>(0)));
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};
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/* ==== generic string representation ==== */
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/** pretty-print an internal C++ type representation
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* @see \ref format-obj.cpp implementation
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*/
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std::string humanReadableTypeID (lib::Literal);
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std::string demangleCxx (lib::Literal rawName);
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/** failsafe human readable type display
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* @return string representing the C++ type.
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* @remarks the purpose of this function is diagnostics
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* and unit-testing. When possible, RTTI is exposed, otherwise
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* the implementation falls back on the static type as seen by
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* the compiler on usage site. An attempt is made to de-mangle
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* and further simplify the type string, leaving out some common
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* (hard wired) namespace prefixes, and stripping typical adornments
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* like `const`, `*` and `&`
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* @warning this function does string transformations behind the scenes,
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* and thus should not be used in performance critical context. Moreover,
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* the returned type string is not necessarily exact and re-parsable.
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*/
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template<typename TY>
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inline std::string
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typeStr (TY const* obj =nullptr) noexcept
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try {
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auto mangledType = obj? typeid(obj).name()
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: typeid(TY).name();
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return humanReadableTypeID (mangledType);
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}
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catch(...)
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{ return "↯"; }
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template<typename TY>
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inline std::string
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typeStr (TY const& ref) noexcept
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{
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return typeStr (&ref);
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}
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}}// namespace lib::meta
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namespace util {
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using lib::meta::typeStr;
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/** failsafe invocation of custom string conversion.
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* @return string to represent the object, by default a [type display](\ref typeStr)
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* @remarks this is a lightweight solution to at least _get any human readable string
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* representation for pretty much every language object._ This minimal solution
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* is defined here, to allow for built-in diagnostics for custom types without
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* the danger of creating much header inclusion and code size bloat. A more
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* elaborate, [extended solution](lib::toString), including _lexical conversions
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* for numbers,_ is defined in format-obj.hpp
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* @note any exceptions during string conversion are caught and silently ignored;
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* the returned string indicates "↯" in this case.
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*/
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template<typename X, typename COND =void>
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struct StringConv
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{
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static std::string
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invoke (X const& x) noexcept
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try { return "«"+typeStr(x)+"»"; }
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catch(...) { return "↯"; }
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};
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template<typename X>
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struct StringConv<X, lib::meta::enable_CustomStringConversion<X>>
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{
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static std::string
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invoke (X const& val) noexcept
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try { return std::string(val); }
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catch(...) { return "↯"; }
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};
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// NOTE: this is meant to be extensible;
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// more specialisations are e.g. in format-obj.hpp
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/** pretty-print a double in fixed-point format */
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std::string showDouble (double) noexcept;
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std::string showFloat (float) noexcept;
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/** pretty-print an address as hex-suffix */
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std::string showAddr (void const* addr) noexcept;
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template<typename X>
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inline std::string
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showAddr (X const& elm) noexcept
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{
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return showAddr(&elm);
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}
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/** diagnostics helper for explicitly indicating pointers */
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template<typename X>
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inline std::string
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showPtr (X* ptr =nullptr)
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{
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return ptr? showAddr(ptr) + " ↗" + StringConv<X>::invoke(*ptr)
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: "⟂ «" + typeStr(ptr) + "»";
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}
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}// namespace util
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#endif /*LIB_META_UTIL_H*/
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