Do not use std::visit() for std::variant

It is not supported for macOS 10.13 and earlier, see https://stackoverflow.com/questions/53946674/noexcept-visitation-for-stdvariant.
ufleisch · Dec 27, 2023 · 7725993 · 7725993
1 parent bd4c9cb
commit 7725993
Showing 1 changed file with 111 additions and 105 deletions.
diff --git a/taglib/toolkit/tvariant.cpp b/taglib/toolkit/tvariant.cpp
@@ -70,125 +70,131 @@ T getVariantValue(StdVariantType *v, bool *ok)
  return {};
 }
 
-// Visitor to print a possibly recursive Variant to an ostream.
-// The representation is JSON with hex strings for ByteVector.
-class OStreamVisitor {
-public:
- OStreamVisitor(std::ostream &os) : s(os)
- {
- }
-
- void operator()(std::monostate v)
- {
- s << "null";
- }
-
- void operator()(bool v)
- {
- s << (v ? "true" : "false");
- }
-
- void operator()(int v)
- {
- s << v;
- }
-
- void operator()(unsigned int v)
- {
- s << v;
- }
-
- void operator()(long long v)
- {
- s << v;
- }
-
- void operator()(unsigned long long v)
- {
- s << v;
+void printStringToStream(std::ostream &s, const String &v)
+{
+ s << '"';
+ for(char c : v.to8Bit(true)) {
+ if(c == '"') {
+ s << "\\\"";
+ }
+ else {
+ s << c;
+ }
  }
+ s << '"';
+}
 
- void operator()(double v)
- {
- s << v;
+void printByteVectorToStream(std::ostream &s, const String &v)
+{
+ s << '"';
+ for(char c : v) {
+ s << "\\x" << std::setfill('0') << std::setw(2) << std::right << std::hex
+ << (static_cast<int>(c) & 0xff);
  }
+ s << std::dec << '"';
+}
 
- void operator()(const TagLib::String &v)
- {
- s << '"';
- for (char c : v.to8Bit(true)) {
- if(c == '"') {
- s << "\\\"";
- }
- else {
- s << c;
- }
+// Print a possibly recursive Variant to an ostream.
+// The representation is JSON with hex strings for ByteVector.
+void printVariantToStream(std::ostream &s, const StdVariantType &v)
+{
+ switch (v.index()) {
+ case Variant::Void:
+ s << "null";
+ break;
+ case Variant::Bool:
+ if(const auto valPtr = std::get_if<Variant::Bool>(&v)) {
+ s << (*valPtr ? "true" : "false");
  }
- s << '"';
- }
-
- void operator()(const TagLib::StringList &v)
- {
- s << '[';
- for(auto it = v.cbegin(); it != v.cend(); ++it) {
- if(it != v.cbegin()) {
- s << ", ";
+ break;
+ case Variant::Int:
+ if(const auto valPtr = std::get_if<Variant::Int>(&v)) {
+ s << *valPtr;
+ }
+ break;
+ case Variant::UInt:
+ if(const auto valPtr = std::get_if<Variant::UInt>(&v)) {
+ s << *valPtr;
+ }
+ break;
+ case Variant::LongLong:
+ if(const auto valPtr = std::get_if<Variant::LongLong>(&v)) {
+ s << *valPtr;
+ }
+ break;
+ case Variant::ULongLong:
+ if(const auto valPtr = std::get_if<Variant::ULongLong>(&v)) {
+ s << *valPtr;
+ }
+ break;
+ case Variant::Double:
+ if(const auto valPtr = std::get_if<Variant::Double>(&v)) {
+ s << *valPtr;
+ }
+ break;
+ case Variant::String:
+ if(const auto valPtr = std::get_if<Variant::String>(&v)) {
+ printStringToStream(s, *valPtr);
+ }
+ break;
+ case Variant::StringList:
+ if(const auto valPtr = std::get_if<Variant::StringList>(&v)) {
+ const auto v = *valPtr;
+ s << '[';
+ for(auto it = valPtr->cbegin(); it != valPtr->cend(); ++it) {
+ if(it != valPtr->cbegin()) {
+ s << ", ";
+ }
+ printStringToStream(s, *it);
  }
- operator()(*it);
+ s << ']';
  }
- s << ']';
- }
-
- void operator()(const TagLib::ByteVector &v)
- {
- s << '"';
- for(char c : v) {
- s << "\\x" << std::setfill('0') << std::setw(2) << std::right << std::hex
- << (static_cast<int>(c) & 0xff);
+ break;
+ case Variant::ByteVector:
+ if(const auto valPtr = std::get_if<Variant::ByteVector>(&v)) {
+ printByteVectorToStream(s, *valPtr);
  }
- s << std::dec << '"';
- }
-
- void operator()(const TagLib::ByteVectorList &v)
- {
- s << '[';
- for(auto it = v.cbegin(); it != v.cend(); ++it) {
- if(it != v.cbegin()) {
- s << ", ";
+ break;
+ case Variant::ByteVectorList:
+ if(const auto valPtr = std::get_if<Variant::ByteVectorList>(&v)) {
+  s << '[';
+  for(auto it = valPtr->cbegin(); it != valPtr->cend(); ++it) {
+  if(it != valPtr->cbegin()) {
+  s << ", ";
+  }
+ printByteVectorToStream(s, *it);
  }
- operator()(*it);
+ s << ']';
  }
- s << ']';
- }
-
- void operator()(const List<TagLib::Variant> &v) {
- s << '[';
- for(auto it = v.cbegin(); it != v.cend(); ++it) {
- if(it != v.cbegin()) {
- s << ", ";
+ break;
+ case Variant::VariantList:
+ if(const auto valPtr = std::get_if<Variant::VariantList>(&v)) {
+ s << '[';
+ for(auto it = valPtr->cbegin(); it != valPtr->cend(); ++it) {
+ if(it != valPtr->cbegin()) {
+ s << ", ";
+ }
+ s << *it;
  }
- s << *it;
+ s << ']';
  }
- s << ']';
- }
-
- void operator()(const Map<TagLib::String, TagLib::Variant> &v)
- {
- s << '{';
- for(auto it = v.cbegin(); it != v.cend(); ++it) {
- if(it != v.cbegin()) {
- s << ", ";
+ break;
+ case Variant::VariantMap:
+ if(const auto valPtr = std::get_if<Variant::VariantMap>(&v)) {
+ s << '{';
+ for(auto it = valPtr->cbegin(); it != valPtr->cend(); ++it) {
+ if(it != valPtr->cbegin()) {
+ s << ", ";
+ }
+ printStringToStream(s, it->first);
+ s << ": ";
+ s << it->second;
  }
- operator()(it->first);
- s << ": ";
- s << it->second;
+ s << '}';
  }
- s << '}';
+ break;
  }
-
-private:
- std::ostream &s;
-};
+}
 
 } // namespace
 
@@ -386,6 +392,6 @@ Variant &Variant::operator=(const Variant &) = default;
 
 std::ostream &operator<<(std::ostream &s, const TagLib::Variant &v)
 {
- std::visit(OStreamVisitor(s), v.d->data);
+ printVariantToStream(s, v.d->data);
  return s;
 }