Use std::string_view and std::optional when possible

.travis.yml

@@ -191,6 +191,31 @@ matrix:
           ./b2 install -d0
           popd
 
+    # C++17 builds
+
+    - compiler: clang
+      env: EXTRAOPTS="--std=c++17" COMPILER=clang++-5.0
+      addons: &clang-50
+        apt:
+          sources:
+            - *sources
+            - llvm-toolchain-trusty-5.0
+          packages:
+            - *packages
+            - clang-5.0
+            - libstdc++-7-dev
+
+    - compiler: gcc
+      env: >
+        EXTRAOPTS="--std=c++17" COMPILER=g++-7 BUILD_ARGS="-j1"
+        EXTRAFLAGS=-Wsuggest-override
+      addons: &gcc-7
+        apt:
+          sources: *sources
+          packages:
+            - *packages
+            - g++-7
+
     # Make-backend builds
 
     - compiler: clang
@@ -223,6 +248,6 @@ before_install:
 script:
   - >
     CXX=${COMPILER} CPPFLAGS="${COMMONFLAGS} ${EXTRAFLAGS}"
-    9k build --vendorize --backend=${BACKEND}
+    9k build --vendorize --backend=${BACKEND} ${EXTRAOPTS}
   - cd build
   - ${BACKEND} test ${BUILD_ARGS}

build.bfg

@@ -8,7 +8,7 @@ project('mettle', version='1.0pre')
 if env.builder('c++').flavor == 'msvc':
     global_options(['/EHsc'], lang='c++')
 else:
-    global_options(['-std=c++14'], lang='c++')
+    global_options(['-std={}'.format(argv.std)], lang='c++')
 
 includes = header_directory('include', include='*.hpp')
 

doc/install.md

@@ -36,8 +36,8 @@ Before you get started with mettle, you'll need to install its dependencies:
 * [bencode.hpp](https://github.com/jimporter/bencode.hpp)
 * [bfg9000](https://jimporter.github.io/bfg9000/)
 
-To simplify the installation of bencode.hpp, you can run
-`scripts/vendorize_bencode.py` from your mettle source directory. This will
+To simplify the installation of bencode.hpp, you can pass `--vendorize` during
+configuration (or run `scripts/vendorize_bencode.py` directly). This will
 download and copy bencode.hpp to mettle's include directory, so you won't have
 to install it yourself.
 
@@ -73,11 +73,15 @@ Building with bfg9000 is straightforward. Just run the following:
 
 ```sh
 cd path/to/mettle/
-9k build/
+9k build/ --vendorize
 cd build/
 ninja install
 ```
 
+As noted above, if you already have bencode.hpp installed, you can remove the
+`--vendorize` argument. If you'd like to build with C++17 support, you can pass
+`--std=c++17` during configuration.
+
 You can specify the compiler to use and its options with the usual (Unix-style)
 environment variables, such as `CXX` and `CXXFLAGS`. For further information
 about how to use bfg9000, such as changing the build backend, see its

include/mettle/driver/detail/optional.hpp

@@ -1,29 +1,28 @@
 #ifndef INC_METTLE_DRIVER_DETAIL_OPTIONAL_HPP
 #define INC_METTLE_DRIVER_DETAIL_OPTIONAL_HPP
 
-// Get _LIBCPP_VERSION to detect libc++.
-#include <ciso646>
+// Try to use std::optional, N4480's optional class, or fall back to Boost's.
 
-// Try to use N4480's optional class, or fall back to Boost's.
-#if defined(METTLE_USE_STDLIB_EXTS)
-#  include <experimental/optional>
-#  define METTLE_OPTIONAL_NS std::experimental
-#elif !defined(METTLE_NO_STDLIB_EXTS) && defined(__has_include)
-   // XXX: clang doesn't support SFINAE in variadic templates, which libstdc++'s
-   // `optional` relies on. See <https://llvm.org/bugs/show_bug.cgi?id=23840>.
-#  if !(defined(__clang__) && !defined(_LIBCPP_VERSION) && \
-        defined(__GLIBCXX__)) && __has_include(<experimental/optional>)
+#ifdef __has_include
+#  if __has_include(<optional>) && __cplusplus >= 201703L
+#    include <optional>
+#    define METTLE_OPTIONAL_NS std
+#  elif __has_include(<experimental/optional>) && \
+        !defined(METTLE_NO_STDLIB_EXTS)
+#    include <experimental/optional>
+#    define METTLE_OPTIONAL_NS std::experimental
+#  endif
+#endif
+
+#ifndef METTLE_OPTIONAL_NS
+#  ifdef METTLE_USE_STDLIB_EXTS
 #    include <experimental/optional>
 #    define METTLE_OPTIONAL_NS std::experimental
 #  else
 #    include <boost/optional.hpp>
 #    include <boost/optional/optional_io.hpp>
 #    define METTLE_OPTIONAL_NS boost
 #  endif
-#else
-#  include <boost/optional.hpp>
-#  include <boost/optional/optional_io.hpp>
-#  define METTLE_OPTIONAL_NS boost
 #endif
 
 #endif

include/mettle/output/detail/string_view.hpp

@@ -0,0 +1,33 @@
+#ifndef INC_METTLE_OUTPUT_DETAIL_STRING_VIEW_HPP
+#define INC_METTLE_OUTPUT_DETAIL_STRING_VIEW_HPP
+
+// Try to use std::string_view, N4480's version, or fall back to Boost's.
+
+#ifdef __has_include
+#  if __has_include(<string_view>) && __cplusplus >= 201703L
+#    include <string_view>
+#    define METTLE_STRING_VIEW std::basic_string_view
+#  elif __has_include(<experimental/string_view>) && \
+        !defined(METTLE_NO_STDLIB_EXTS)
+#    include <experimental/string_view>
+#    define METTLE_STRING_VIEW std::experimental::basic_string_view
+#  endif
+#endif
+
+#ifndef METTLE_STRING_VIEW
+#  ifdef METTLE_USE_STDLIB_EXTS
+#    include <experimental/string_view>
+#    define METTLE_STRING_VIEW std::experimental::basic_string_view
+#  else
+#    include <boost/version.hpp>
+#    if BOOST_VERSION >= 106100
+#      include <boost/utility/string_view.hpp>
+#      define METTLE_STRING_VIEW boost::basic_string_view
+#    else
+#      include <boost/utility/string_ref.hpp>
+#      define METTLE_STRING_VIEW boost::basic_string_ref
+#    endif
+#  endif
+#endif
+
+#endif

include/mettle/output/string.hpp

@@ -1,22 +1,7 @@
 #ifndef INC_METTLE_OUTPUT_STRING_HPP
 #define INC_METTLE_OUTPUT_STRING_HPP
 
-// Try to use N4480's string_view class, or fall back to Boost's.
-#if defined(METTLE_USE_STDLIB_EXTS)
-#  include <boost/utility/string_ref.hpp>
-#  define METTLE_STRING_VIEW boost::basic_string_ref
-#elif !defined(METTLE_NO_STDLIB_EXTS) && defined(__has_include)
-#  if __has_include(<experimental/string_view>)
-#    include <experimental/string_view>
-#    define METTLE_STRING_VIEW std::experimental::basic_string_view
-#  else
-#    include <boost/utility/string_ref.hpp>
-#    define METTLE_STRING_VIEW boost::basic_string_ref
-#  endif
-#else
-#  include <boost/utility/string_ref.hpp>
-#  define METTLE_STRING_VIEW boost::basic_string_ref
-#endif
+#include "detail/string_view.hpp"
 
 #include <codecvt>
 #include <ostream>

options.bfg

@@ -2,3 +2,4 @@
 
 argument('vendorize', action='store_true',
          help='vendorize the bencode library')
+argument('std', default='c++14', help='set the C++ standard to compile with')

src/libmettle/cmd_line.cpp

@@ -19,7 +19,7 @@
 #endif
 
 #if __cplusplus >= 201703L
-#  define FALLTHROUGH [[fallthrough]]
+#  define FALLTHROUGH [[fallthrough]];
 #elif defined(__clang__)
 #  define FALLTHROUGH [[clang::fallthrough]];
 #elif defined(__GNUG__) && __GNUC__ >= 7

test/suite/test_test_caller.cpp

@@ -3,6 +3,8 @@ using namespace mettle;
 
 #include "run_counter.hpp"
 
+// Check if std::apply exists, and if not, use our own implementation.
+#if __cplusplus < 201703L
 template<typename F, typename Tuple, std::size_t ...I>
 decltype(auto) apply_impl(F &&f, Tuple &&t, std::index_sequence<I...>) {
   return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
@@ -15,6 +17,7 @@ decltype(auto) apply(F&& f, Tuple &&t) {
   >;
   return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
 }
+#endif
 
 template<typename Tuple>
 struct run_counter_from_tuple_t;