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In retrospect, I wish C++ used the term "alias" instead of "reference" to be very clear that a pointer or similar underlying mechanism, including storage, is not necessary.
"It is unspecified whether or not a reference requires storage."
https://eel.is/c++draft/dcl.ref#4
The issue now (and not really C++'s fault) is that people coming from a language like Java hear "reference" and think it works the same way in C++ as it does in Java. Especially reference parameters. 
eel.is[dcl.ref]
![Screenshot a slide. Black text on white.
Top-left: some fine print
Slide title: Constant References
Slide body as follows:
• A const qualified reference is a read-only alias
– const int& r = i; //r is a read-only alias of an int i
– r = 3; //compile-time error
• The referent cannot be overwritten or altered using a const reference to it
– const std::string& r = s; //s is std::string instance
– r = "it"; //can't overwrite referent via const ref
– r[0] = 'a'; //can't modify referent via const ref
• A final Java reference can change the referent but the reference variable itself cannot be assigned to
– const or not, a C++ reference can never be “rebound”
• C++ reference is quite different from Java reference
Bottom right: 106](https://media.hachyderm.io/media_attachments/files/111/031/010/103/063/015/original/28731b0dc0a7073d.png "Screenshot a slide. Black text on white.
Top-left: some fine print
Slide title: Constant References
Slide body as follows:
• A const qualified reference is a read-only alias
– const int& r = i; //r is a read-only alias of an int i
– r = 3; //compile-time error
• The referent cannot be overwritten or altered using a const reference to it
– const std::string& r = s; //s is std::string instance
– r = \"it\"; //can't overwrite referent via const ref
– r[0] = 'a'; //can't modify referent via const ref
• A final Java reference can change the referent but the reference variable itself cannot be assigned to
– const or not, a C++ reference can never be “rebound”
• C++ reference is quite different from Java reference
Bottom right: 106")
An illustration, a couple of exercises, and an example comparing references in C++ and Java (and Python). 
(This is also when I wish more students were on Mastodon/Fediverse. I don't know how but we need to collectively work on that.)
![Screenshot of a slide. Black text on white.
Top-left: some fine print
Slide title: Illustration 3: References in Java
Slide body as follows:
• An object var is an object reference; not an object
– Initializing an object variable w object copies a reference
– String s1 = "it"; //RHS is unnamed object, LHS is obj ref
[a boxes and arrow diagram]
• Assigning an object var to another obj var copies the reference, making both vars point to the same object
– String s2 = s1; //s1 and s2 both point to the same obj
[a boxes and arrow diagram]
• An object w no references is “garbage” (collected)
– s1 = "no"; //s1 points to new obj; only s2 points to "it"
– s2 = "hi"; //"it" is now garbage, can be collected
[a boxes and arrow diagram]
Bottom right: 103](https://media.hachyderm.io/media_attachments/files/111/031/254/686/028/240/original/25990a58c8b3d221.png "Screenshot of a slide. Black text on white.
Top-left: some fine print
Slide title: Illustration 3: References in Java
Slide body as follows:
• An object var is an object reference; not an object
– Initializing an object variable w object copies a reference
– String s1 = \"it\"; //RHS is unnamed object, LHS is obj ref
[a boxes and arrow diagram]
• Assigning an object var to another obj var copies the reference, making both vars point to the same object
– String s2 = s1; //s1 and s2 both point to the same obj
[a boxes and arrow diagram]
• An object w no references is “garbage” (collected)
– s1 = \"no\"; //s1 points to new obj; only s2 points to \"it\"
– s2 = \"hi\"; //\"it\" is now garbage, can be collected
[a boxes and arrow diagram]
Bottom right: 103")
![Screenshot of a slide. Black text on white.
Top-left: some fine print
Top-right:
It can help to draw “boxes and arrows” diagrams as in Illustration 3
Slide title: Exercise 3: What Prints?
Slide body as follows:
[2 panes showing code in a dark theme: left pane has Java code; right pane has Python code. Code shown at end.]
What are the final values of the variables x, y, s1, and s2? Why?
Bottom right: 104
Java code, left pane:
String s1 = "it";
String s2 = "no";
String x = s1;
String y = s2;
String t = x; //what is being attempted?
x = y;
y = t;
System.out.printf("%s %s\n", x, y); // ?
System.out.printf("%s %s", s1, s2); // ?
Python code, right pane:
s1 = "it"
s2 = "no"
x = s1
y = s2
t = x
x = y
y = t
print(x, y) # ?
print(s1, s2); # ?](https://media.hachyderm.io/media_attachments/files/111/031/261/378/734/799/original/c3372a5373f21f32.png "Screenshot of a slide. Black text on white.
Top-left: some fine print
Top-right:
It can help to draw “boxes and arrows” diagrams as in Illustration 3
Slide title: Exercise 3: What Prints?
Slide body as follows:
[2 panes showing code in a dark theme: left pane has Java code; right pane has Python code. Code shown at end.]
What are the final values of the variables x, y, s1, and s2? Why?
Bottom right: 104
Java code, left pane:
String s1 = \"it\";
String s2 = \"no\";
String x = s1;
String y = s2;
String t = x; //what is being attempted?
x = y;
y = t;
System.out.printf(\"%s %s\n\", x, y); // ?
System.out.printf(\"%s %s\", s1, s2); // ?
Python code, right pane:
s1 = \"it\"
s2 = \"no\"
x = s1
y = s2
t = x
x = y
y = t
print(x, y) # ?
print(s1, s2); # ?")
![Screenshot of a slide. Black text on white.
Top-left: some fine print
Top-right:
Full example online: https://sigcpp.godbolt.org/z/jY5ETbzcT
Slide title: Example 22: Compare C++ and Java References
Slide body as follows:
[2 panes showing code in a dark theme: left pane has C++ code; right pane has Java code. The code is at the URL shown in top-right corner of slide.]
Observe the differences on Lines 7, 11, 13, 14, 16, 17, 18, and 20
Bottom right: 107](https://media.hachyderm.io/media_attachments/files/111/031/262/586/185/239/original/df069bcffc44d763.png "Screenshot of a slide. Black text on white.
Top-left: some fine print
Top-right:
Full example online: https://sigcpp.godbolt.org/z/jY5ETbzcT
Slide title: Example 22: Compare C++ and Java References
Slide body as follows:
[2 panes showing code in a dark theme: left pane has C++ code; right pane has Java code. The code is at the URL shown in top-right corner of slide.]
Observe the differences on Lines 7, 11, 13, 14, 16, 17, 18, and 20
Bottom right: 107")
