QString's allocation behaviour is inconsistent for empty string constructions

Consider the following cases in Qt 5.13.1:

QString a;               // 1, isNull() == true
QString b("");           // 2, isNull() == false
QString::fromUtf8("");   // 3, isNull() == false
QString::fromLatin1(""); // 4, isNull() == false

It seems that QString does dynamic memory allocation in cases 2 and 3 (which are effectively the same cases given the specification of const char* constructor), but not in cases 1 and 4.

• Is there reason to ever allocate for empty string?
• Should fromUtf8() and fromLatin1() behave differently with respect to memory allocation when given empty string?

Technical details:

• fromLatin1(): calls fromLatin1_helper() which in case of zero-sized string calls

  d = Data::allocate(0);

  Data is a typedef of QStringData (a typedef forQTypedArrayData<ushort> defined in qstringliteral.h), and Data::allocate() returns qt_array_empty (or qt_array_unsharable_empty) given the zero-valued parameter.

• fromUtf8(): calls fromUtf8_helper() -> QUtf8::convertToUnicode("", 0) -> QString result(0, Qt::Uninitialized); -> d = Data::allocate(0 + 1);