Expressions and Operators

Question 1

What is an expression?

Answer 1

An expression is a chunk of Ruby code that the Ruby interpreter can evaluate to produce a value.

Question 2

What does the keyword “self” evaluate to?

Answer 2

the current object

Question 3

What does the __FILE__ evaluate to?

Answer 3

a string that names the file that the Ruby interpreter is executing

Question 4

What does __LINE__ evaluate to?

Answer 4

an integer that specifies the line number within __FILE__ of the current line of code.

Question 5

What are the 4 kinds of variables in Ruby?

Answer 5

• global (begin with $)
• instance variables (begin with @)
• class variables (being with @@)
• local variables (begin with _ or lowercase letter)

Question 6

What does it mean if :: appears in an expression?

Answer 6

It usually means a reference to a constant but might also indicate a method.

Question 7

What error is thrown if you use a class variable before it is initialized?

Answer 7

NameError

Question 8

What does Ruby return with an uninitialized instance variable?

Question 9

What does an unitialized global variable evaluate to?

Question 10

What error is thrown if you try to use an identifier that does not have a local variable or a method associated with it?

Answer 10

NameError

Question 11

The Ruby interpreter enforces the constancy of constants. T/F?

Answer 11

False. It only issues a warning if the value of the constant is changed.

Question 12

What does :: do in a compound expression?

Answer 12

It separates the name of the constant from the class or module in which it is defined.

Question 13

Constants can be defined in nested namespaces like this:
Conversions::Area::HECTATRES_PER_ACRE

T/F?

Question 14

What ahppened if the left hand side is omitted from :: in a constant reference?

Answer 14

The constant is looked up in the global scope.