Rust Quiz 3:🔸increment ref count 🔸question mark operator 🔸legal comment signs 🔸patterm matching ignore sign 🔸type requirements

This week’s 5-questions carousel hits:
🔸increment ref count
🔸question mark operator
🔸legal comment signs
🔸patterm matching ignore sign
🔸type requirements

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1. Rust Friday 3
A question lead guide to learn Rust

2. API
The smart pointers Rc and Arc provide reference counting. What is
the API for incrementing a reference count?
➔.add()
➔.incr()
➔.clone()
➔.increment()

3. .clone()
The API for incrementing a reference count using the smart pointers Rc and Arc in Rust is
.clone().
In Rust, Rc (Reference Counting) and Arc (Atomically Reference Counted) are smart
pointers that allow multiple ownership of data by keeping track of the number of references
to a value. When a new reference is created, the reference count is incremented, and
when a reference is dropped, the reference count is decremented. When the reference
count reaches zero, the value is deallocated.
To increment the reference count of a value in Rust, you can use the .clone() method
on the Rc or Arc smart pointer. This method creates a new reference to the same value,
incrementing the reference count by one.
Therefore, the correct API for incrementing a reference count using the smart pointers Rc
and Arc in Rust is .clone().

4. API
What happens when an error occurs that is being handled by the
question mark (?) operator?

➔The error is reported and execution continues.
➔An exception is raised. The effect(s) of the exception are
defined by the error! macro.
➔The program panics immediately.
➔Rust attempts to convert the error to the local function's
error type and return it as Result::Err. If that fails, the
program panics.

5. Rust attempts to convert the error to the local function's error
type and return it as Result::Err. If that fails, the program
panics.


When an error occurs that is being handled by the question mark ? operator in Rust, the error is
propagated up the call stack until it is handled by a matching catch block, or until it reaches the
top level of the program and causes the program to terminate with an error message.
Specifically, when the ? operator is used, Rust attempts to convert the error to the local
function's error type and return it as Result::Err. If the error can be converted successfully,
the Result::Err value is returned from the function, and the calling code can continue to
handle the error. If the error cannot be converted to the local error type, Rust will panic with a
message indicating that the error could not be converted.
Therefore, the correct answer is: Rust attempts to convert the error to the local function's error
type and return it as Result::Err. If that fails, the program panics.

6. Syntax
Which comment syntax is not legal?



➔/*
➔#
➔//!
➔//

7. #




The comment syntax that is not legal in Rust is #.
In Rust, there are two types of comments: line comments and block comments. Line
comments start with // and continue to the end of the line. Block comments start with /*
and end with */. These comments can be nested.
The //! syntax is a special type of line comment that is used to document the enclosing
item (module, crate, function, etc.). However, the # symbol is not a valid character to start
a comment in Rust, and attempting to use it will result in a syntax error.
Therefore, the correct answer is #.

8. Syntax
In matching patterns, values are
ignored with ___.



➔.ignore()
➔an underscore (_)
➔..
➔skip

9. an underscore (_)




In matching patterns, values are ignored using an underscore (_) character.
In Rust, the underscore character (_) is used as a wildcard pattern that matches any value. When used in a
matching pattern, the underscore indicates that the value being matched against should be ignored, and
execution should continue as if the value were matched successfully.
For example, in the following code:
let x = Some(5);
match x {
Some(_) => println!("Some"),
None => println!("None"),
}
The underscore in the Some(_) pattern indicates that the value contained in the Some variant should be
ignored, and the println!("Some") statement should be executed regardless of the value.
Therefore, the correct answer is an underscore (_).

10. Type
Defining a ___ requires a lifetime parameter.



➔function that ends the lifetime of one of its
arguments
➔struct that contains a reference to a value
➔function with a generic argument
➔struct that contains a reference to a boxed value

11. struct that contains a reference to a value




Defining a struct that contains a reference to a value requires a lifetime parameter in Rust.
In Rust, lifetimes are a way of describing the relationship between references and the values they refer to. A
lifetime parameter is a way of explicitly indicating that a reference in a struct or function has a specific lifetime
that must be respected.
When a struct contains a reference to a value, it is important to ensure that the reference is not invalidated
before the struct is dropped. This is typically done by specifying a lifetime parameter on the struct definition.
For example, consider the following code:
struct MyStruct<'a> {
my_ref: &'a i32,
}
In this example, the lifetime parameter 'a is used to indicate that the reference my_ref has the same lifetime
as the struct MyStruct. This ensures that the reference remains valid for the lifetime of the struct.
Therefore, the correct answer is "struct that contains a reference to a value".

12. https://bit.ly/udemyrust