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Commit 37f9c933 authored by Francesco Giacomini's avatar Francesco Giacomini
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frames.tex

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%\includeonlyframes{current} \includeonlyframes{current}
\begin{frame} \begin{frame}
\tikz [remember picture,overlay] \tikz [remember picture,overlay]
...@@ -286,7 +286,7 @@ bool less(int n, int m) \{ return n < m; \}\end{codeblock} ...@@ -286,7 +286,7 @@ bool less(int n, int m) \{ return n < m; \}\end{codeblock}
\begin{codeblock} \begin{codeblock}
\uncover<1->{std::array<int,3> a = \{123, 456, 789\};} \uncover<1->{std::array<int,3> a = \{123, 456, 789\};}
\uncover<2->{\alert<2>{auto first = a.begin();} // or std::begin(a)} \uncover<2->{\alert<2>{auto first = a.begin();} // or std::begin(a)}
\uncover<3->{\alert<3>{auto \alt<14>{\alert{const }}{}last = a.end();}\alt<14>{}{ } // or std::end(a)} \uncover<3->{\alert<3>{auto \only<14->{\alert{const }}last = a.end();}\only<-13>{ } // or std::end(a)}
\uncover<4->{while (\alert<4,7,10,13>{first != last}) \{ \uncover<4->{while (\alert<4,7,10,13>{first != last}) \{
... \alert<5,8,11>{*first} ...; ... \alert<5,8,11>{*first} ...;
\alert<6,9,12>{++first}; \alert<6,9,12>{++first};
...@@ -380,7 +380,7 @@ find(Iterator first, Iterator last, const T\& value) ...@@ -380,7 +380,7 @@ find(Iterator first, Iterator last, const T\& value)
\begin{itemize} \begin{itemize}
\item Examples \item Examples
\begin{codeblock} \begin{codeblock}
std::vector<int> v = { 2, 5, 4, 0, 1 }; std::vector<int> v = \{ 2, 5, 4, 0, 1 \};
// sort the first half of the vector in ascending order // sort the first half of the vector in ascending order
std::sort(std::begin(v), std::begin(v) + v.size() / 2); std::sort(std::begin(v), std::begin(v) + v.size() / 2);
...@@ -595,8 +595,8 @@ accumulate(\ldots, ...@@ -595,8 +595,8 @@ accumulate(\ldots,
\uncover<2->{class SomeUniqueName \{ \uncover<2->{class SomeUniqueName \{
\uncover<5->{int v\_;} \uncover<5->{int v\_;}
public: public:
explicit SomeUniqueName(\uncover<5->{int v}) \uncover<5->{explicit SomeUniqueName(int v)
\uncover<5->{: v\_\{v\}} \{\} : v\_\{v\} \{\}}
\alt<-7>{auto}{\alert<8>{int }} operator()\uncover<3->{(int i) \alt<-7>{auto}{\alert<8>{int }} operator()\uncover<3->{(int i)
\{ return i + v\uncover<5->{\_}; \}} \{ return i + v\uncover<5->{\_}; \}}
\};} \};}
...@@ -1171,6 +1171,513 @@ auto s = std::shared\_ptr<FILE>\{ ...@@ -1171,6 +1171,513 @@ auto s = std::shared\_ptr<FILE>\{
\end{columns} \end{columns}
\end{frame} \end{frame}
\begin{frame}
\begin{itemize}
\item Try the code snippets
\item C++ and Memory $\rightarrow$ Pointers
\item Adapt the previous exercises to use smart pointers
\item Starting from \code{dir.cpp}, write code to:
\begin{itemize}
\item create a smart pointer managing a \code{DIR} resource obtained with
the \code{opendir} function call
\item associate a deleter to that smart pointer
\item implement a function to read the names of the files in that directory
\item check if the deleter is called at the right moment
\item hide the creation of the smart pointer behind a factory function
\item populate a vector of FILEs, properly wrapped in a smart pointer,
obtained opening the regular files in that directory
\item \ldots
\end{itemize}
\end{itemize}
\end{frame}
\section{Move semantics}
\begin{frame}[fragile,label=current]{Copy vs move}
\begin{columns}
\begin{column}{.45\textwidth}
\begin{codeblock}{\tiny
class String \{
char* s\_;
\ldots
\};}\end{codeblock}
\begin{codeblock}<1->{\tiny
String s1\{"Hi!"\};
\uncover<2->{String s2\{s1\};}}\end{codeblock}
\uncover<3->{\small
\begin{itemize}
\item Both \code{s1} and \code{s2} exist at the end
\item The ``deep'' copy is needed
\end{itemize}
}
\begin{codeblock}<4->{\tiny
String get\_string() \{ return "Hey"; \}
String \alert<6>{s3}\{\alert<5>{get\_string()}\}\alert<7>{;}}\end{codeblock}
\uncover<8->{\small
\begin{itemize}
\item Only \code{s3} exists at the end
\item The ``deep'' copy is a waste
\end{itemize}
}
\end{column}
\begin{column}{.55\textwidth}
\newcommand*{\stackx}{0.}
\newcommand*{\heapx}{3.0}
\begin{tikzpicture}
[anchor=south west]
\node at (\stackx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize stack}}
] {};
\node at (\heapx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize heap}}
] {};
\node at (\heapx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hi!\char`\\0};
\node at (\heapx,5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4abc}}
] {};
\node at (\stackx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s1}},
] {};
\node at (\stackx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4abc};
\visible<2->{
\node at (\heapx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hi!\char`\\0};
\node at (\heapx,4) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4ab0}}
] (r2) {};
\node at (\stackx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s2}},
] {};
\node at (\stackx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] (h2) {\scriptsize\tt 0x4ab0};
%\draw[arrow] (h2) -- (r2);
}
\visible<6->{
\node at (\heapx-0.1,2.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,2.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hey\char`\\0};
\node at (\heapx,2.5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4aac}}
] {};
\node at (\stackx-0.1,2.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s3}},
] {};
\node at (\stackx,2.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4aac};
}
\visible<5-6>{
\node at (\heapx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hey\char`\\0};
\node at (\heapx,1.5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4aa0}}
] {};
\node at (\stackx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
] {};
\node at (\stackx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4aa0};
}
\end{tikzpicture}
\end{column}
\end{columns}
\end{frame}
\begin{frame}[fragile,label=current]{Copy vs move \insertcontinuationtext}
\begin{columns}
\begin{column}{.45\textwidth}
\begin{codeblock}{\tiny
\uncover<1->{class String \{
char* s\_;
public:
String(char const* s) \{
size\_t size = strlen(s) + 1;
s\_ = new char[size];
memcpy(s\_, s, size);
\}
~String() \{ delete [] s\_; \}}
\uncover<2->{ // \alert<2>{copy}
String(String const& other) \{
size\_t size = strlen(other.s\_) + 1;
s\_ = new char[size];
memcpy(s\_, other.s\_, size);
\}}
\uncover<4->{ // \alert<4-5>{move}
String(\alert<7>{???} tmp): s\_(tmp.s\_) \{
\uncover<5->{ tmp.s\_ = nullptr;}
\}}
\uncover<1->{ \ldots
\};
String s1\{"Hi!"\};}
\uncover<2->{String s2\{s1\};}
\uncover<3->{String \alert<4>{s3}\{\alert<3>{get\_string()}\}\alert<6>{;}}
}\end{codeblock}
\end{column}
\begin{column}{.55\textwidth}
\newcommand*{\stackx}{0.}
\newcommand*{\heapx}{3.0}
\begin{tikzpicture}
[anchor=south west]
\node at (\stackx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize stack}}
] {};
\node at (\heapx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize heap}}
] {};
\node at (\heapx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hi!\char`\\0};
\node at (\heapx,5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4abc}}
] {};
\node at (\stackx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s1}},
] {};
\node at (\stackx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4abc};
\visible<2->{
\node at (\heapx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hi!\char`\\0};
\node at (\heapx,4) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4ab0}}
] (r2) {};
\node at (\stackx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s2}},
] {};
\node at (\stackx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] (h2) {\scriptsize\tt 0x4ab0};
%\draw[arrow] (h2) -- (r2);
}
\visible<4->{
\node at (\stackx-0.1,2.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt s3}},
] {};
\node at (\stackx,2.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt \alert<4>{0x4aa0}};
}
\visible<3->{
\node at (\heapx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt Hey\char`\\0};
\node at (\heapx,1.5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4aa0}}
] {};
}
\visible<3-5>{
\node at (\stackx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
] {};
\node at (\stackx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt \alt<3-4>{\alert<4>{0x4aa0}}{\code{\alert<5>{nullptr}}}};
}
\end{tikzpicture}
\end{column}
\end{columns}
\end{frame}
\begin{frame}[label=current]{lvalues vs rvalues}
\begin{itemize}
\item The taxonomy of values in C++ is complex
\begin{itemize}
\item glvalue, prvalue, xvalue, lvalue, rvalue
\end{itemize}
\item We can assume
\begin{description}
\item [lvalue] A named object
\begin{itemize}
\item for which you can take the address
\item \alert{l} stands for ``left'' because it used to represent the
\alert{l}eft-hand side of an assignment
\end{itemize}
\item [rvalue] An unnamed (temporary) object
\begin{itemize}
\item for which you can't take the address
\item \alert{r} stands for ``right'' because it used to represent the
\alert{r}ight-hand side of an assignment
\end{itemize}
\end{description}
\end{itemize}
\end{frame}
\begin{frame}[fragile,label=current]{Rvalue reference}
\begin{itemize}
\item A \texttt{T\&\&} is an rvalue reference
\begin{itemize}
\item introduced in C++11
\end{itemize}
\item It binds to rvalues but not to lvalues
\end{itemize}
\begin{codeblock}<2->{\tiny
class Thing;
Thing make\_thing();
Thing t;
\uncover<3->{Thing & r = t;}\uncover<4->{ // ok}
\uncover<5->{Thing && r = t;}\uncover<6->{ // error}
\uncover<7->{Thing & r = make\_thing();}\uncover<8->{ // error}
\uncover<9->{Thing && r = make\_thing();}\uncover<10->{ // ok}
\uncover<11->{Thing const& r = make\_thing();}\uncover<12->{ // ok (!)}
\uncover<13->{Thing const&& r = make\_thing();}\uncover<14->{ // ok, but what for?}}\end{codeblock}
\begin{codeblock}<15->{\tiny
class String \{
// move constructor
String(String\alert<15>{&&} tmp) : s\_(tmp.s\_) \{
tmp.s\_ = nullptr;
\}
\};
String s2\{s1\}; // call String::String(String const&)
String s3\{get\_string()\}; // call String::String(String&&)}\end{codeblock}
\end{frame}
\begin{frame}[fragile,label=current]{Rvalue reference \insertcontinuationtext}
\begin{itemize}
\item Any function can accept rvalue references
\begin{codeblock}
void foo(String&&);
foo(get\_string());
foo(String\{"hello"\});\end{codeblock}
\item lvalues can be explicitly transformed into rvalues
\begin{codeblock}
String s;
foo(s); // error
foo(std::move(s)); // ok, I don't care any more about s
s.size(); // dangerous\end{codeblock}
\end{itemize}
\end{frame}
\begin{frame}[fragile]{Smart pointers \insertcontinuationtext} \begin{frame}[fragile]{Smart pointers \insertcontinuationtext}
\begin{columns}[c] \begin{columns}[c]
...@@ -2099,241 +2606,6 @@ Handle h1\{10\}, h2\{20\}; ...@@ -2099,241 +2606,6 @@ Handle h1\{10\}, h2\{20\};
arrow/.style={->} arrow/.style={->}
} }
\begin{frame}[fragile]{Copy vs move}
\begin{columns}
\begin{column}{.45\textwidth}
\begin{codeblock}<1->
Handle h1\{123\};
\uncover<2->{Handle h2\{h1\};}\end{codeblock}
\uncover<3->{\small
\begin{itemize}
\item Both \texttt{h1} and \texttt{h2} exist at the end
\item The ``deep'' copy is needed
\end{itemize}
}
\begin{codeblock}<4->
Handle make\_holder();
Handle \alert<6>{h3}\{\alert<5>{make\_holder()}\}\alert<7>{;}\end{codeblock}
\uncover<8->{\small
\begin{itemize}
\item Only \texttt{h3} exists at the end
\item The ``deep'' copy is a waste
\item Could reuse the ``guts'' of the temporary
\end{itemize}
}
\end{column}
\begin{column}{.55\textwidth}
\newcommand*{\stackx}{0.}
\newcommand*{\heapx}{3.0}
\begin{tikzpicture}
[anchor=south west]
\node at (\stackx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize stack}}
] {};
\node at (\heapx,0) [
rectangle,
minimum width=2cm,
minimum height=7cm,
draw=black,
label={90:{\scriptsize heap}}
] {};
\node at (\heapx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt 123};
\node at (\heapx,5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4abc}}
] {};
\node at (\stackx-0.1,4.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt h1}},
] {};
\node at (\stackx,5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4abc};
\visible<2->{
\node at (\heapx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt 123};
\node at (\heapx,4) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4ab0}}
] (r2) {};
\node at (\stackx-0.1,3.9) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt h2}},
] {};
\node at (\stackx,4) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] (h2) {\scriptsize\tt 0x4ab0};
%\draw[arrow] (h2) -- (r2);
}
\visible<6->{
\node at (\heapx-0.1,2.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,2.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt 456};
\node at (\heapx,2.5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4aac}}
] {};
\node at (\stackx-0.1,2.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
label={180:{\scriptsize\tt h3}},
] {};
\node at (\stackx,2.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4aac};
}
\visible<5-6>{
\node at (\heapx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=0.7cm,
] {};
\node at (\heapx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white
] {\scriptsize\tt 456};
\node at (\heapx,1.5) [
rectangle,
minimum width=.5cm,
minimum height=.5cm,
draw=black,
densely dotted,
label={270:{\scriptsize\tt 0x4aa0}}
] {};
\node at (\stackx-0.1,1.4) [
rectangle,
fill=green!10!white,
draw=black!40,
minimum width=2.2cm,
minimum height=.7cm,
] {};
\node at (\stackx,1.5) [
rectangle,
minimum width=2cm,
minimum height=.5cm,
draw=black,
fill=green!30!white,
] {\scriptsize\tt 0x4aa0};
}
\end{tikzpicture}
\end{column}
\end{columns}
\end{frame}
\section{Move semantics}
\begin{frame}{lvalues vs rvalues}
\begin{itemize}
\item The taxonomy of values in C++ is complex
\begin{itemize}
\item glvalue, prvalue, xvalue, lvalue, rvalue
\end{itemize}
\item We can assume
\begin{description}
\item [lvalue] A named object
\begin{itemize}
\item for which you can take the address
\item \alert{l} stands for ``left'' because it used to represent the
\alert{l}eft-hand side of an assignment
\end{itemize}
\item [rvalue] An unnamed (temporary) object
\begin{itemize}
\item for which you can't take the address
\item \alert{r} stands for ``right'' because it used to represent the
\alert{r}ight-hand side of an assignment
\end{itemize}
\end{description}
\end{itemize}
\end{frame}
\begin{frame}[fragile]{Move constructor} \begin{frame}[fragile]{Move constructor}
\begin{columns} \begin{columns}
...@@ -2447,33 +2719,6 @@ Handle \alert<3-5>{h\{}\alert<2>{make\_holder()}\alert<3-5>{\}}\alert<6>{;}\end{ ...@@ -2447,33 +2719,6 @@ Handle \alert<3-5>{h\{}\alert<2>{make\_holder()}\alert<3-5>{\}}\alert<6>{;}\end{
\end{frame} \end{frame}
\begin{frame}[fragile]{Rvalue reference}
\begin{itemize}
\item A \texttt{T\&\&} is an rvalue reference
\item It binds to rvalues but not to lvalues
\end{itemize}
\begin{codeblock}<2->{
class Thing;
Thing make\_thing();
Thing t;
\uncover<3->{Thing & r = t;}\uncover<4->{ // ok}
\uncover<5->{Thing && r = t;}\uncover<6->{ // error}
\uncover<7->{Thing & r = make\_thing();}\uncover<8->{ // error}
\uncover<9->{Thing && r = make\_thing();}\uncover<10->{ // ok}
\uncover<11->{Thing const& r = make\_thing();}\uncover<12->{ // ok (!)}
\uncover<13->{Thing const&& r = make\_thing();}\uncover<14->{ // ok, but what for?}}\end{codeblock}
\uncover<15->{
\begin{itemize}
\item A reference extends the lifetime of a temporary object until the end of the scope
\end{itemize}
}
\end{frame}
\begin{frame}[fragile]{Move assignment} \begin{frame}[fragile]{Move assignment}
\begin{columns} \begin{columns}
......
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