shiboken: Refactor generation of sequence access methods

Rename writeStdListWrapperMethods() to
writeDefaultSequenceMethods() since that is is more close to its
purpose. In the function, get the base container type.

Use std::advance instead of a loop to position the iterator.
This is specialized for random access iterators to perform an
addition and thus more efficient.

Use const_iterator in __getitem__ to prevent Qt containers from
detaching.

Task-number: PYSIDE-904
Change-Id: I4735f39193c4f4efa856440ecddbc48b3a5071ae
Reviewed-by: Christian Tismer <tismer@stackless.com>

2 files changed, 13 insertions, 8 deletions

diff --git a/sources/shiboken2/generator/shiboken2/cppgenerator.cpp b/sources/shiboken2/generator/shiboken2/cppgenerator.cpp
index cf9d4508f..52892663e 100644
--- a/sources/shiboken2/generator/shiboken2/cppgenerator.cpp
+++ b/sources/shiboken2/generator/shiboken2/cppgenerator.cpp
@@ -328,6 +328,7 @@ void CppGenerator::generateClass(QTextStream &s, const GeneratorContext &classCo
         s << "#include <algorithm>\n#include <set>\n";
     if (metaClass->generateExceptionHandling())
         s << "#include <exception>\n";
+    s << "#include <iterator>\n"; // For containers
 
     if (wrapperDiagnostics())
         s << "#include <helper.h>\n#include <iostream>\n";
@@ -4134,7 +4135,7 @@ void CppGenerator::writeSequenceMethods(QTextStream &s,
     }
 
     if (!injectedCode)
-        writeStdListWrapperMethods(s, context);
+        writeDefaultSequenceMethods(s, context);
 }
 
 void CppGenerator::writeTypeAsSequenceDefinition(QTextStream &s, const AbstractMetaClass *metaClass)
@@ -6062,7 +6063,7 @@ void CppGenerator::writeHashFunction(QTextStream &s, const GeneratorContext &con
     s<< "}\n\n";
 }
 
-void CppGenerator::writeStdListWrapperMethods(QTextStream &s, const GeneratorContext &context)
+void CppGenerator::writeDefaultSequenceMethods(QTextStream &s, const GeneratorContext &context)
 {
     const AbstractMetaClass *metaClass = context.metaClass();
     ErrorCode errorCode(0);
@@ -6080,8 +6081,10 @@ void CppGenerator::writeStdListWrapperMethods(QTextStream &s, const GeneratorCon
     writeCppSelfDefinition(s, context);
     writeIndexError(s, QLatin1String("index out of bounds"));
 
-    s << INDENT << metaClass->qualifiedCppName() << "::iterator _item = " << CPP_SELF_VAR << "->begin();\n";
-    s << INDENT << "for (Py_ssize_t pos = 0; pos < _i; pos++) _item++;\n";
+    QString value;
+    s << INDENT << metaClass->qualifiedCppName() << "::const_iterator _item = "
+        << CPP_SELF_VAR << "->begin();\n"
+        << INDENT << "std::advance(_item, _i);\n";
 
     const AbstractMetaTypeList instantiations = metaClass->templateBaseClassInstantiations();
     if (instantiations.isEmpty()) {
@@ -6115,9 +6118,11 @@ void CppGenerator::writeStdListWrapperMethods(QTextStream &s, const GeneratorCon
     s << INDENT << "}\n";
     writeArgumentConversion(s, itemType, QLatin1String("cppValue"), QLatin1String("pyArg"), metaClass);
 
-    s << INDENT << metaClass->qualifiedCppName() << "::iterator _item = " << CPP_SELF_VAR << "->begin();\n";
-    s << INDENT << "for (Py_ssize_t pos = 0; pos < _i; pos++) _item++;\n";
-    s << INDENT << "*_item = cppValue;\n";
+    s << INDENT << metaClass->qualifiedCppName() << "::iterator _item = "
+        << CPP_SELF_VAR << "->begin();\n"
+        << INDENT << "std::advance(_item, _i);\n"
+        << INDENT << "*_item = cppValue;\n";
+
     s << INDENT << "return {};\n";
     s << "}\n";
 }
diff --git a/sources/shiboken2/generator/shiboken2/cppgenerator.h b/sources/shiboken2/generator/shiboken2/cppgenerator.h
index 5fe67be21..7308f7d18 100644
--- a/sources/shiboken2/generator/shiboken2/cppgenerator.h
+++ b/sources/shiboken2/generator/shiboken2/cppgenerator.h
@@ -344,7 +344,7 @@ private:
     void writeHashFunction(QTextStream &s, const GeneratorContext &context);
 
     /// Write default implementations for sequence protocol
-    void writeStdListWrapperMethods(QTextStream &s, const GeneratorContext &context);
+    void writeDefaultSequenceMethods(QTextStream &s, const GeneratorContext &context);
     /// Helper function for writeStdListWrapperMethods.
     void writeIndexError(QTextStream &s, const QString &errorMsg);