Fix compilation errors with libc++ on QNX 7

This patch fixes the compilation errors on QNX 7:
1) QNX 7 compiler (i.e qcc based GCC 5.4.0 with libc++ from LLVM) has a
limited c++11 feature support and causing the compilation
errors with the inheriting constructors. This fixes the issues by
providing the required constructors explicitly.

2) Resolves an ambiguous overload error with optional<T>

3 files changed, 15 insertions, 15 deletions

diff --git a/src/mbgl/style/expression/interpolate.cpp b/src/mbgl/style/expression/interpolate.cpp
index 852042382c..54fbc6e1d7 100644
--- a/src/mbgl/style/expression/interpolate.cpp
+++ b/src/mbgl/style/expression/interpolate.cpp
@@ -170,23 +170,23 @@ ParseResult parseInterpolate(const Convertible& value, ParsingContext& ctx) {
             labelValue->match(
                 [&](uint64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](int64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](double n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{n};
                     }
                 },
                 [&](const auto&) {}
diff --git a/src/mbgl/style/expression/match.cpp b/src/mbgl/style/expression/match.cpp
index 340f1dab4d..4b4984811f 100644
--- a/src/mbgl/style/expression/match.cpp
+++ b/src/mbgl/style/expression/match.cpp
@@ -138,7 +138,7 @@ optional<InputType> parseInputValue(const Convertible& input, ParsingContext& pa
                     parentContext.error("Branch labels must be integers no larger than " + util::toString(Value::maxSafeInteger()) + ".", index);
                 } else {
                     type = {type::Number};
-                    result = {static_cast<int64_t>(n)};
+                    result = optional<InputType>{static_cast<int64_t>(n)};
                 }
             },
             [&] (int64_t n) {
@@ -146,7 +146,7 @@ optional<InputType> parseInputValue(const Convertible& input, ParsingContext& pa
                     parentContext.error("Branch labels must be integers no larger than " + util::toString(Value::maxSafeInteger()) + ".", index);
                 } else {
                     type = {type::Number};
-                    result = {n};
+                    result = optional<InputType>{n};
                 }
             },
             [&] (double n) {
@@ -156,7 +156,7 @@ optional<InputType> parseInputValue(const Convertible& input, ParsingContext& pa
                     parentContext.error("Numeric branch labels must be integer values.", index);
                 } else {
                     type = {type::Number};
-                    result = {static_cast<int64_t>(n)};
+                    result = optional<InputType>{static_cast<int64_t>(n)};
                 }
             },
             [&] (const std::string& s) {
diff --git a/src/mbgl/style/expression/step.cpp b/src/mbgl/style/expression/step.cpp
index ee6055091e..a1ca0a702e 100644
--- a/src/mbgl/style/expression/step.cpp
+++ b/src/mbgl/style/expression/step.cpp
@@ -127,23 +127,23 @@ ParseResult Step::parse(const mbgl::style::conversion::Convertible& value, Parsi
             labelValue->match(
                 [&](uint64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](int64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](double n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{n};
                     }
                 },
                 [&](const auto&) {}