Merge pull request #21 from xsco/enh/std-optional-support

Use `std::optional` or experimental as available

28 files changed, 565 insertions, 490 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea07846..73d9df2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,7 +6,7 @@
 # The meson/ninja build should be preferred in all other cases.
 #
 cmake_minimum_required(VERSION 3.10)
-project(libdjinterop VERSION 0.11.0)
+project(libdjinterop VERSION 0.12.0)
 
 # Require C++17
 set(CMAKE_CXX_STANDARD 17)
@@ -18,6 +18,14 @@ find_package(SQLite3 3.11.0 REQUIRED)
 # Require zlib >= 1.2.8
 find_package(ZLIB 1.2.8 REQUIRED)
 
+# Generate config.hpp based on build-time environment.
+include(CheckIncludeFileCXX)
+CHECK_INCLUDE_FILE_CXX(optional DJINTEROP_STD_OPTIONAL)
+CHECK_INCLUDE_FILE_CXX(experimental/optional DJINTEROP_STD_EXPERIMENTAL_OPTIONAL)
+configure_file(
+    include/djinterop/config.hpp.in
+    include/djinterop/config.hpp)
+
 add_library(
     djinterop
     src/djinterop/enginelibrary/el_crate_impl.cpp
@@ -50,6 +58,7 @@ target_include_directories(
     ${SQLite3_INCLUDE_DIRS}
     ${ZLIB_INCLUDE_DIRS}
     ext/sqlite_modern_cpp
+    ${CMAKE_CURRENT_BINARY_DIR}/include
     include src)
 
 target_link_libraries(
@@ -60,7 +69,7 @@ target_link_libraries(
 install(TARGETS djinterop DESTINATION lib)
 install(FILES
     include/djinterop/album_art.hpp
-    include/djinterop/config.hpp
+    ${CMAKE_CURRENT_BINARY_DIR}/include/djinterop/config.hpp
     include/djinterop/crate.hpp
     include/djinterop/database.hpp
     include/djinterop/djinterop.hpp
diff --git a/example/engine_prime.cpp b/example/engine_prime.cpp
index d7b8520..ac81bef 100644
--- a/example/engine_prime.cpp
+++ b/example/engine_prime.cpp
@@ -54,7 +54,7 @@ int main(int argc, char** argv)
     tr.set_year(1970);
     tr.set_title("Some Song"s);
     tr.set_artist("Some Artist"s);
-    tr.set_publisher(std::nullopt);  // std::nullopt indicates missing metadata
+    tr.set_publisher(djinterop::stdx::nullopt);  // indicates missing metadata
     tr.set_key(djinterop::musical_key::a_minor);
     tr.set_bitrate(320);
     tr.set_average_loudness(0.5);  // loudness range (0, 1]
@@ -73,7 +73,7 @@ int main(int argc, char** argv)
     tr.set_adjusted_main_cue(2732);  // manually adjusted
 
     // There are always 8 hot cues, whereby each can optionally be set
-    std::array<std::optional<djinterop::hot_cue>, 8> cues;
+    std::array<djinterop::stdx::optional<djinterop::hot_cue>, 8> cues;
     cues[0] = djinterop::hot_cue{
         "Cue 1", 1377924.5,  // position in number of samples
         el::standard_pad_colors::pad_1};
diff --git a/include/djinterop/config.hpp b/include/djinterop/config.hpp.in
index 97260cc..b558501 100644
--- a/include/djinterop/config.hpp
+++ b/include/djinterop/config.hpp.in
@@ -46,4 +46,10 @@
 #endif  // DJINTEROP_SOURCE
 #define DJINTEROP_LOCAL DJINTEROP_SYMBOL_LOCAL
 
+// Symbols defined after this point represent the environment at the time
+// that this library was built.  The environment when this library is used must
+// be compatible in order to use the library successfully.
+#cmakedefine DJINTEROP_STD_OPTIONAL
+#cmakedefine DJINTEROP_STD_EXPERIMENTAL_OPTIONAL
+
 #endif  // DJINTEROP_CONFIG_HPP
diff --git a/include/djinterop/crate.hpp b/include/djinterop/crate.hpp
index 8a961ce..b0d7d85 100644
--- a/include/djinterop/crate.hpp
+++ b/include/djinterop/crate.hpp
@@ -23,11 +23,11 @@ Lesser General Public License for more details.
 
 #include <cstdint>
 #include <memory>
-#include <optional>
 #include <string>
 #include <vector>
 
 #include <djinterop/config.hpp>
+#include <djinterop/optional.hpp>
 
 namespace djinterop
 {
@@ -111,7 +111,7 @@ public:
     ///
     /// If the crate doesn't have a parent, then `djinterop::nullopt` is
     /// returned.
-    std::optional<crate> parent() const;
+    stdx::optional<crate> parent() const;
 
     /// Removes a track from the crate
     ///
@@ -126,12 +126,12 @@ public:
     ///
     /// If `djinterop::nullopt` is given, then this crate will have no parent.
     /// That is, it becomes a root crate.
-    void set_parent(std::optional<crate> parent) const;
+    void set_parent(stdx::optional<crate> parent) const;
 
     /// Gets the sub-crate of this one with a given name.
     ///
     /// If no such crate is found, then `djinterop::nullopt` is returned.
-    std::optional<crate> sub_crate_by_name(const std::string& name) const;
+    stdx::optional<crate> sub_crate_by_name(const std::string& name) const;
 
     /// Returns the crate's contained tracks
     std::vector<track> tracks() const;
diff --git a/include/djinterop/database.hpp b/include/djinterop/database.hpp
index 9f68d61..b947733 100644
--- a/include/djinterop/database.hpp
+++ b/include/djinterop/database.hpp
@@ -25,17 +25,12 @@
 
 #include <cstdint>
 #include <memory>
-#include <optional>
 #include <stdexcept>
 #include <string>
 #include <vector>
 
 #include <djinterop/config.hpp>
-
-namespace sqlite
-{
-class database;
-}
+#include <djinterop/optional.hpp>
 
 namespace djinterop
 {
@@ -70,9 +65,9 @@ public:
 
     /// Returns the crate with the given ID
     ///
-    /// If no such crate exists in the database, then `djinterop::std::nullopt`
+    /// If no such crate exists in the database, then `djinterop::stdx::nullopt`
     /// is returned.
-    std::optional<crate> crate_by_id(int64_t id) const;
+    stdx::optional<crate> crate_by_id(int64_t id) const;
 
     /// Returns all crates contained in the database
     std::vector<crate> crates() const;
@@ -125,8 +120,8 @@ public:
 
     /// Returns the root-level crate with the given name.
     ///
-    /// If no such crate exists, then `djinterop::std::nullopt` is returned.
-    std::optional<crate> root_crate_by_name(const std::string& name) const;
+    /// If no such crate exists, then `djinterop::stdx::nullopt` is returned.
+    stdx::optional<crate> root_crate_by_name(const std::string& name) const;
 
     /// Returns all root crates contained in the database
     ///
@@ -135,9 +130,9 @@ public:
 
     /// Returns the track with the given id
     ///
-    /// If no such track exists in the database, then `djinterop::std::nullopt`
+    /// If no such track exists in the database, then `djinterop::stdx::nullopt`
     /// is returned.
-    std::optional<track> track_by_id(int64_t id) const;
+    stdx::optional<track> track_by_id(int64_t id) const;
 
     /// Returns all tracks whose `relative_path` attribute in the database
     /// matches the given string
diff --git a/include/djinterop/meson.build b/include/djinterop/meson.build
new file mode 100644
index 0000000..c43a0b2
--- /dev/null
+++ b/include/djinterop/meson.build
@@ -0,0 +1,20 @@
+# Generate config file based on build-time feature detection.
+# Note that most build configuration for public headers is handled in the
+# parent build file; this file exists solely because the `output` parameter
+# of configure_file() does not, at the time of writing (meson 0.55.0), support
+# writing the output file to a different directory.
+conf_data = configuration_data()
+if cpp_compiler.has_header('optional')
+    conf_data.set10('DJINTEROP_STD_OPTIONAL', true)
+endif
+if cpp_compiler.has_header('experimental/optional')
+    conf_data.set10('DJINTEROP_STD_EXPERIMENTAL_OPTIONAL', true)
+endif
+configure_file(
+    input: 'config.hpp.in',
+    output: 'config.hpp',
+    configuration: conf_data,
+    format: 'cmake',
+    install_dir: get_option('includedir') + '/djinterop'
+)
+
diff --git a/include/djinterop/optional.hpp b/include/djinterop/optional.hpp
new file mode 100644
index 0000000..6795913
--- /dev/null
+++ b/include/djinterop/optional.hpp
@@ -0,0 +1,63 @@
+/*
+    This file is part of libdjinterop.
+
+    libdjinterop is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    libdjinterop is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with libdjinterop.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+#ifndef DJINTEROP_OPTIONAL_HPP
+#define DJINTEROP_OPTIONAL_HPP
+
+#include <djinterop/config.hpp>
+
+#ifdef DJINTEROP_STD_OPTIONAL
+
+#include <optional>
+
+namespace djinterop
+{
+namespace stdx
+{
+using std::bad_optional_access;
+using std::in_place;
+using std::in_place_t;
+using std::make_optional;
+using std::nullopt;
+using std::nullopt_t;
+using std::optional;
+}  // namespace stdx
+}  // namespace djinterop
+
+#elif DJINTEROP_STD_EXPERIMENTAL_OPTIONAL
+#include <experimental/optional>
+
+namespace djinterop
+{
+namespace stdx
+{
+using std::experimental::bad_optional_access;
+using std::experimental::in_place;
+using std::experimental::in_place_t;
+using std::experimental::make_optional;
+using std::experimental::nullopt;
+using std::experimental::nullopt_t;
+using std::experimental::optional;
+}  // namespace stdx
+}  // namespace djinterop
+
+#else
+#error This library requires support for optional<T>, but none was found
+#endif
+
+#endif  // DJINTEROP_OPTIONAL_HPP
diff --git a/include/djinterop/track.hpp b/include/djinterop/track.hpp
index e058fd0..ff649cc 100644
--- a/include/djinterop/track.hpp
+++ b/include/djinterop/track.hpp
@@ -27,13 +27,13 @@
 #include <chrono>
 #include <cstdint>
 #include <memory>
-#include <optional>
 #include <stdexcept>
 #include <string>
 #include <vector>
 
 #include <djinterop/config.hpp>
 #include <djinterop/musical_key.hpp>
+#include <djinterop/optional.hpp>
 #include <djinterop/performance_data.hpp>
 #include <djinterop/semantic_version.hpp>
 
@@ -90,10 +90,10 @@ public:
     void set_adjusted_main_cue(double sample_offset) const;
 
     /// Returns the album name (metadata) of the track
-    std::optional<std::string> album() const;
+    stdx::optional<std::string> album() const;
 
     /// Sets the album name (metadata) of the track
-    void set_album(std::optional<std::string> album) const;
+    void set_album(stdx::optional<std::string> album) const;
     void set_album(std::string album) const;
 
     /// Returns the ID of the `album_art` associated to the track
@@ -101,51 +101,51 @@ public:
     /// If the track doesn't have an associated `album_art`, then `nullopt`
     /// is returned.
     /// TODO (haslersn): Return an `album_art` object instead.
-    std::optional<int64_t> album_art_id() const;
+    stdx::optional<int64_t> album_art_id() const;
 
     /// Sets the ID of the `album_art` associated to the track
     /// TODO (haslersn): Pass an `album_art` object instead.
-    void set_album_art_id(std::optional<int64_t> album_art_id) const;
+    void set_album_art_id(stdx::optional<int64_t> album_art_id) const;
     void set_album_art_id(int64_t album_art_id) const;
 
     /// Returns the artist (metadata) of the track
-    std::optional<std::string> artist() const;
+    stdx::optional<std::string> artist() const;
 
     /// Sets the artist (metadata) of the track
-    void set_artist(std::optional<std::string> artist) const;
+    void set_artist(stdx::optional<std::string> artist) const;
     void set_artist(std::string artist) const;
 
-    std::optional<double> average_loudness() const;
+    stdx::optional<double> average_loudness() const;
 
-    void set_average_loudness(std::optional<double> average_loudness) const;
+    void set_average_loudness(stdx::optional<double> average_loudness) const;
     void set_average_loudness(double average_loudness) const;
 
     /// Returns the bitrate (metadata) of the track
-    std::optional<int64_t> bitrate() const;
+    stdx::optional<int64_t> bitrate() const;
 
     /// Sets the bitrate (metadata) of the track
-    void set_bitrate(std::optional<int64_t> bitrate) const;
+    void set_bitrate(stdx::optional<int64_t> bitrate) const;
     void set_bitrate(int64_t bitrate) const;
 
     /// Returns the BPM (metadata) of the track, rounded to the nearest integer
-    std::optional<double> bpm() const;
+    stdx::optional<double> bpm() const;
 
     /// Sets the BPM (metadata) of the track, rounded to the nearest integer
-    void set_bpm(std::optional<double> bpm) const;
+    void set_bpm(stdx::optional<double> bpm) const;
     void set_bpm(double bpm) const;
 
     /// Returns the comment associated to the track (metadata)
-    std::optional<std::string> comment() const;
+    stdx::optional<std::string> comment() const;
 
     /// Sets the comment associated to the track (metadata)
-    void set_comment(std::optional<std::string> comment) const;
+    void set_comment(stdx::optional<std::string> comment) const;
     void set_comment(std::string comment) const;
 
     /// Returns the composer (metadata) of the track
-    std::optional<std::string> composer() const;
+    stdx::optional<std::string> composer() const;
 
     /// Sets the composer (metadata) of the track
-    void set_composer(std::optional<std::string> composer) const;
+    void set_composer(stdx::optional<std::string> composer) const;
     void set_composer(std::string composer) const;
 
     /// Returns the crates containing the track
@@ -163,7 +163,7 @@ public:
     void set_default_main_cue(double sample_offset) const;
 
     /// Returns the duration (metadata) of the track
-    std::optional<std::chrono::milliseconds> duration() const;
+    stdx::optional<std::chrono::milliseconds> duration() const;
 
     /// Returns the file extension part of `track::relative_path()`
     ///
@@ -175,20 +175,20 @@ public:
     std::string filename() const;
 
     /// Returns the genre (metadata) of the track
-    std::optional<std::string> genre() const;
+    stdx::optional<std::string> genre() const;
 
     /// Sets the genre (metadata) of the track
-    void set_genre(std::optional<std::string> genre) const;
+    void set_genre(stdx::optional<std::string> genre) const;
     void set_genre(std::string genre) const;
 
-    std::optional<hot_cue> hot_cue_at(int32_t index) const;
+    stdx::optional<hot_cue> hot_cue_at(int32_t index) const;
 
-    void set_hot_cue_at(int32_t index, std::optional<hot_cue> cue) const;
+    void set_hot_cue_at(int32_t index, stdx::optional<hot_cue> cue) const;
     void set_hot_cue_at(int32_t index, hot_cue cue) const;
 
-    std::array<std::optional<hot_cue>, 8> hot_cues() const;
+    std::array<stdx::optional<hot_cue>, 8> hot_cues() const;
 
-    void set_hot_cues(std::array<std::optional<hot_cue>, 8> cues) const;
+    void set_hot_cues(std::array<stdx::optional<hot_cue>, 8> cues) const;
 
     /// Returns the ID of this track
     ///
@@ -197,33 +197,33 @@ public:
     int64_t id() const;
 
     /// TODO (haslersn): Document this method.
-    std::optional<track_import_info> import_info() const;
+    stdx::optional<track_import_info> import_info() const;
 
     /// TODO (haslersn): Document these methods.
     void set_import_info(
-        const std::optional<track_import_info>& import_info) const;
+        const stdx::optional<track_import_info>& import_info) const;
     void set_import_info(const track_import_info& import_info) const;
 
     /// Returns `true` iff `*this` is valid as described in the class comment
     bool is_valid() const;
 
     /// Returns the key (metadata) of the track
-    std::optional<musical_key> key() const;
+    stdx::optional<musical_key> key() const;
 
     /// Sets the key (metadata) of the track
-    void set_key(std::optional<musical_key> key) const;
+    void set_key(stdx::optional<musical_key> key) const;
     void set_key(musical_key key) const;
 
     /// Get the time at which this track was last accessed
     ///
     /// Note that on VFAT filesystems, the access time is ceiled to just a date,
     /// and loses any time precision.
-    std::optional<std::chrono::system_clock::time_point> last_accessed_at()
+    stdx::optional<std::chrono::system_clock::time_point> last_accessed_at()
         const;
 
     /// TODO (haslersn): Document these methods.
     void set_last_accessed_at(
-        std::optional<std::chrono::system_clock::time_point> last_accessed_at)
+        stdx::optional<std::chrono::system_clock::time_point> last_accessed_at)
         const;
     void set_last_accessed_at(
         std::chrono::system_clock::time_point last_accessed_at) const;
@@ -232,40 +232,41 @@ public:
     ///
     /// Note that this is the attribute modification time, not the data
     /// modification time, i.e. ctime not mtime.
-    std::optional<std::chrono::system_clock::time_point> last_modified_at()
+    stdx::optional<std::chrono::system_clock::time_point> last_modified_at()
         const;
 
     /// TODO (haslersn): Document these methods.
     void set_last_modified_at(
-        std::optional<std::chrono::system_clock::time_point> last_modified_at)
+        stdx::optional<std::chrono::system_clock::time_point> last_modified_at)
         const;
     void set_last_modified_at(
         std::chrono::system_clock::time_point last_modified_at) const;
 
     /// Returns the time at which the track was last played
-    std::optional<std::chrono::system_clock::time_point> last_played_at() const;
+    stdx::optional<std::chrono::system_clock::time_point> last_played_at()
+        const;
 
     /// Sets the time at which the track was last played
     void set_last_played_at(
-        std::optional<std::chrono::system_clock::time_point> time) const;
+        stdx::optional<std::chrono::system_clock::time_point> time) const;
     void set_last_played_at(std::chrono::system_clock::time_point time) const;
 
-    std::optional<loop> loop_at(int32_t index) const;
+    stdx::optional<loop> loop_at(int32_t index) const;
 
-    void set_loop_at(int32_t index, std::optional<loop> l) const;
+    void set_loop_at(int32_t index, stdx::optional<loop> l) const;
     void set_loop_at(int32_t index, loop l) const;
 
-    std::array<std::optional<loop>, 8> loops() const;
+    std::array<stdx::optional<loop>, 8> loops() const;
 
-    void set_loops(std::array<std::optional<loop>, 8> loops) const;
+    void set_loops(std::array<stdx::optional<loop>, 8> loops) const;
 
     std::vector<waveform_entry> overview_waveform() const;
 
     /// Returns the publisher (metadata) of the track
-    std::optional<std::string> publisher() const;
+    stdx::optional<std::string> publisher() const;
 
     /// Sets the publisher (metadata) of the track
-    void set_publisher(std::optional<std::string> publisher) const;
+    void set_publisher(stdx::optional<std::string> publisher) const;
     void set_publisher(std::string publisher) const;
 
     /// Get the required number of samples per waveform entry.
@@ -284,23 +285,23 @@ public:
     /// TODO (haslersn): Document this method.
     void set_relative_path(std::string relative_path) const;
 
-    std::optional<sampling_info> sampling() const;
+    stdx::optional<sampling_info> sampling() const;
 
-    void set_sampling(std::optional<sampling_info> sample_rate) const;
+    void set_sampling(stdx::optional<sampling_info> sample_rate) const;
     void set_sampling(sampling_info sample_rate) const;
 
     /// Returns the title (metadata) of the track
-    std::optional<std::string> title() const;
+    stdx::optional<std::string> title() const;
 
     /// Sets the title (metadata) of the track
-    void set_title(std::optional<std::string> title) const;
+    void set_title(stdx::optional<std::string> title) const;
     void set_title(std::string title) const;
 
     /// Returns the track number (metadata) of the track
-    std::optional<int32_t> track_number() const;
+    stdx::optional<int32_t> track_number() const;
 
     /// Sets the track number (metadata) of the track
-    void set_track_number(std::optional<int32_t> track_number) const;
+    void set_track_number(stdx::optional<int32_t> track_number) const;
     void set_track_number(int32_t track_number) const;
 
     std::vector<waveform_entry> waveform() const;
@@ -308,10 +309,10 @@ public:
     void set_waveform(std::vector<waveform_entry> waveform) const;
 
     /// Returns the recording year (metadata) of the track
-    std::optional<int32_t> year() const;
+    stdx::optional<int32_t> year() const;
 
     /// Sets the recording year (metadata) of the track
-    void set_year(std::optional<int32_t> year) const;
+    void set_year(stdx::optional<int32_t> year) const;
     void set_year(int32_t year) const;
 
     // TODO (haslersn): non public?
diff --git a/include/meson.build b/include/meson.build
index ee89840..3d6595c 100644
--- a/include/meson.build
+++ b/include/meson.build
@@ -1,12 +1,15 @@
+# Used only to generate config.hpp in the nested include dir.
+subdir('djinterop')
+
 djinterop_header_files = [
     'djinterop/album_art.hpp',
-    'djinterop/config.hpp',
     'djinterop/crate.hpp',
     'djinterop/database.hpp',
     'djinterop/djinterop.hpp',
     'djinterop/exceptions.hpp',
     'djinterop/enginelibrary.hpp',
     'djinterop/musical_key.hpp',
+    'djinterop/optional.hpp',
     'djinterop/pad_color.hpp',
     'djinterop/performance_data.hpp',
     'djinterop/semantic_version.hpp',
diff --git a/meson.build b/meson.build
index e34ffcb..575e12f 100644
--- a/meson.build
+++ b/meson.build
@@ -1,7 +1,7 @@
 project(
     'djinterop',
     'cpp', 'c',
-    version: '0.11.0',
+    version: '0.12.0',
     license: 'LGPL-3.0',
     default_options: ['cpp_std=c++17', 'default_library=both'])
 
diff --git a/src/djinterop/crate.cpp b/src/djinterop/crate.cpp
index 5da4ad3..4f3fdaf 100644
--- a/src/djinterop/crate.cpp
+++ b/src/djinterop/crate.cpp
@@ -80,7 +80,7 @@ std::string crate::name() const
     return pimpl_->name();
 }
 
-std::optional<crate> crate::parent() const
+stdx::optional<crate> crate::parent() const
 {
     return pimpl_->parent();
 }
@@ -95,13 +95,12 @@ void crate::set_name(std::string name) const
     pimpl_->set_name(name);
 }
 
-void crate::set_parent(std::optional<crate> parent) const
+void crate::set_parent(stdx::optional<crate> parent) const
 {
     pimpl_->set_parent(parent);
 }
 
-std::optional<crate> crate::sub_crate_by_name(
-    const std::string& name) const
+stdx::optional<crate> crate::sub_crate_by_name(const std::string& name) const
 {
     return pimpl_->sub_crate_by_name(name);
 }
diff --git a/src/djinterop/database.cpp b/src/djinterop/database.cpp
index 1a224f8..fcff0d3 100644
--- a/src/djinterop/database.cpp
+++ b/src/djinterop/database.cpp
@@ -37,7 +37,7 @@ transaction_guard database::begin_transaction() const
     return pimpl_->begin_transaction();
 }
 
-std::optional<crate> database::crate_by_id(int64_t id) const
+stdx::optional<crate> database::crate_by_id(int64_t id) const
 {
     return pimpl_->crate_by_id(id);
 }
@@ -92,13 +92,13 @@ std::vector<crate> database::root_crates() const
     return pimpl_->root_crates();
 }
 
-std::optional<crate> database::root_crate_by_name(
+stdx::optional<crate> database::root_crate_by_name(
     const std::string& name) const
 {
     return pimpl_->root_crate_by_name(name);
 }
 
-std::optional<track> database::track_by_id(int64_t id) const
+stdx::optional<track> database::track_by_id(int64_t id) const
 {
     return pimpl_->track_by_id(id);
 }
diff --git a/src/djinterop/enginelibrary/el_crate_impl.cpp b/src/djinterop/enginelibrary/el_crate_impl.cpp
index f3a2360..0567b02 100644
--- a/src/djinterop/enginelibrary/el_crate_impl.cpp
+++ b/src/djinterop/enginelibrary/el_crate_impl.cpp
@@ -54,7 +54,6 @@ using djinterop::track;
 //     relationship is not written to this table.
 namespace
 {
-
 void update_path(
     sqlite::database& music_db, crate cr, const std::string& parent_path)
 {
@@ -85,8 +84,8 @@ void ensure_valid_name(const std::string& name)
 
 }  // namespace
 
-el_crate_impl::el_crate_impl(std::shared_ptr<el_storage> storage, int64_t id)
-    : crate_impl{id}, storage_{std::move(storage)}
+el_crate_impl::el_crate_impl(std::shared_ptr<el_storage> storage, int64_t id) :
+    crate_impl{id}, storage_{std::move(storage)}
 {
 }
 
@@ -133,9 +132,7 @@ crate el_crate_impl::create_sub_crate(std::string name)
     el_transaction_guard_impl trans{storage_};
 
     std::string path;
-    storage_->db
-            << "SELECT path FROM Crate WHERE id = ?"
-            << id() >>
+    storage_->db << "SELECT path FROM Crate WHERE id = ?" << id() >>
         [&](std::string path_val) {
             if (path.empty())
             {
@@ -157,13 +154,12 @@ crate el_crate_impl::create_sub_crate(std::string name)
                     "crateParentId) VALUES (?, ?)"
                  << sub_id << id();
 
-    storage_->db
-        << "INSERT INTO CrateHierarchy (crateId, crateIdChild) "
-           "SELECT crateId, ? FROM CrateHierarchy "
-           "WHERE crateIdChild = ? "
-           "UNION "
-           "SELECT ? AS crateId, ? AS crateIdChild"
-        << sub_id << id() << id() << sub_id;
+    storage_->db << "INSERT INTO CrateHierarchy (crateId, crateIdChild) "
+                    "SELECT crateId, ? FROM CrateHierarchy "
+                    "WHERE crateIdChild = ? "
+                    "UNION "
+                    "SELECT ? AS crateId, ? AS crateIdChild"
+                 << sub_id << id() << id() << sub_id;
 
     crate cr{std::make_shared<el_crate_impl>(storage_, sub_id)};
 
@@ -211,7 +207,7 @@ bool el_crate_impl::is_valid()
 
 std::string el_crate_impl::name()
 {
-    std::optional<std::string> name;
+    stdx::optional<std::string> name;
     storage_->db << "SELECT title FROM Crate WHERE id = ?" << id() >>
         [&](std::string title) {
             if (!name)
@@ -231,9 +227,9 @@ std::string el_crate_impl::name()
     return *name;
 }
 
-std::optional<crate> el_crate_impl::parent()
+stdx::optional<crate> el_crate_impl::parent()
 {
-    std::optional<crate> parent;
+    stdx::optional<crate> parent;
     storage_->db
             << "SELECT crateParentId FROM CrateParentList WHERE crateOriginId "
                "= ? AND crateParentId <> crateOriginId"
@@ -298,7 +294,7 @@ void el_crate_impl::set_name(std::string name)
     trans.commit();
 }
 
-void el_crate_impl::set_parent(std::optional<crate> parent)
+void el_crate_impl::set_parent(stdx::optional<crate> parent)
 {
     el_transaction_guard_impl trans{storage_};
 
@@ -323,9 +319,9 @@ void el_crate_impl::set_parent(std::optional<crate> parent)
     trans.commit();
 }
 
-std::optional<crate> el_crate_impl::sub_crate_by_name(const std::string& name)
+stdx::optional<crate> el_crate_impl::sub_crate_by_name(const std::string& name)
 {
-    std::optional<crate> cr;
+    stdx::optional<crate> cr;
     storage_->db << "SELECT cr.id FROM Crate cr "
                     "JOIN CrateParentList cpl ON (cpl.crateOriginId = cr.id) "
                     "WHERE cr.title = ? "
diff --git a/src/djinterop/enginelibrary/el_crate_impl.hpp b/src/djinterop/enginelibrary/el_crate_impl.hpp
index 55a24df..7b67835 100644
--- a/src/djinterop/enginelibrary/el_crate_impl.hpp
+++ b/src/djinterop/enginelibrary/el_crate_impl.hpp
@@ -41,11 +41,11 @@ public:
     std::vector<crate> descendants() override;
     bool is_valid() override;
     std::string name() override;
-    std::optional<crate> parent() override;
+    stdx::optional<crate> parent() override;
     void remove_track(track tr) override;
     void set_name(std::string name) override;
-    void set_parent(std::optional<crate> parent) override;
-    std::optional<crate> sub_crate_by_name(const std::string& name) override;
+    void set_parent(stdx::optional<crate> parent) override;
+    stdx::optional<crate> sub_crate_by_name(const st