Introduce to_array() to fix building on macOS

A previous incarnation, make_array, existed in basejob.cpp before.
The new direction taken by C++20 is to either deduce the array (but
the used Apple standard library doesn't have deduction guides yet) or
to use to_array() that converts a C array to std::array. This latter
option is taken here, with to_array() defined in quotient_common.h
until we move over to C++20.

2 files changed, 25 insertions, 15 deletions

diff --git a/lib/jobs/basejob.cpp b/lib/jobs/basejob.cpp
index 9a7b9b5e..400a9243 100644
--- a/lib/jobs/basejob.cpp
+++ b/lib/jobs/basejob.cpp
@@ -5,6 +5,7 @@
 #include "basejob.h"
 
 #include "connectiondata.h"
+#include "quotient_common.h"
 
 #include <QtCore/QRegularExpression>
 #include <QtCore/QTimer>
@@ -15,8 +16,6 @@
 #include <QtNetwork/QNetworkReply>
 #include <QtNetwork/QNetworkRequest>
 
-#include <array>
-
 using namespace Quotient;
 using std::chrono::seconds, std::chrono::milliseconds;
 using namespace std::chrono_literals;
@@ -63,12 +62,6 @@ QDebug BaseJob::Status::dumpToLog(QDebug dbg) const
     return dbg << ": " << message;
 }
 
-template <typename... Ts>
-constexpr auto make_array(Ts&&... items)
-{
-    return std::array<std::common_type_t<Ts...>, sizeof...(Ts)>({items...});
-}
-
 class BaseJob::Private {
 public:
     struct JobTimeoutConfig {
@@ -163,8 +156,8 @@ public:
     {
         // FIXME: use std::array {} when Apple stdlib gets deduction guides for it
         static const auto verbs =
-            make_array(QStringLiteral("GET"), QStringLiteral("PUT"),
-                       QStringLiteral("POST"), QStringLiteral("DELETE"));
+            to_array({ QStringLiteral("GET"), QStringLiteral("PUT"),
+                       QStringLiteral("POST"), QStringLiteral("DELETE") });
         const auto verbWord = verbs.at(size_t(verb));
         return verbWord % ' '
                % (reply ? reply->url().toString(QUrl::RemoveQuery)
diff --git a/lib/quotient_common.h b/lib/quotient_common.h
index 789128cf..037d5ded 100644
--- a/lib/quotient_common.h
+++ b/lib/quotient_common.h
@@ -8,6 +8,24 @@
 namespace Quotient {
 Q_NAMESPACE
 
+namespace impl {
+    template <class T, std::size_t N, std::size_t... I>
+    constexpr std::array<std::remove_cv_t<T>, N>
+        to_array_impl(T (&&a)[N], std::index_sequence<I...>)
+    {
+        return { {std::move(a[I])...} };
+    }
+}
+// std::array {} needs explicit template parameters on macOS because
+// Apple stdlib doesn't have deduction guides for std::array; to alleviate that,
+// to_array() is borrowed from C++20 (thanks to cppreference for the possible
+// implementation: https://en.cppreference.com/w/cpp/container/array/to_array)
+template <typename T, size_t N>
+constexpr auto to_array(T (&& items)[N])
+{
+    return impl::to_array_impl(std::move(items), std::make_index_sequence<N>{});
+}
+
 // TODO: code like this should be generated from the CS API definition
 
 //! \brief Membership states
@@ -29,10 +47,9 @@ enum class Membership : unsigned int {
 Q_DECLARE_FLAGS(MembershipMask, Membership)
 Q_FLAG_NS(MembershipMask)
 
-constexpr inline std::array MembershipStrings = {
+constexpr inline auto MembershipStrings = to_array(
     // The order MUST be the same as the order in the original enum
-    "join", "leave", "invite", "knock", "ban"
-};
+    { "join", "leave", "invite", "knock", "ban" });
 
 //! \brief Local user join-state names
 //!
@@ -49,10 +66,10 @@ enum class JoinState : std::underlying_type_t<Membership> {
 Q_DECLARE_FLAGS(JoinStates, JoinState)
 Q_FLAG_NS(JoinStates)
 
-constexpr inline std::array JoinStateStrings {
+constexpr inline auto JoinStateStrings = to_array({
     MembershipStrings[0], MembershipStrings[1], MembershipStrings[2],
     MembershipStrings[3] /* same as MembershipStrings, sans "ban" */
-};
+});
 
 //! \brief Network job running policy flags
 //!