Hash creation with symbols and strings in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a hash in Ruby?

A hash is a collection of key-value pairs, like a dictionary, where you can look up a value using its key.

beginner

How do you create a hash with symbol keys in Ruby?

You can create it using curly braces and symbol keys with colons, like: { name: "Alice", age: 30 }.

beginner

How do you create a hash with string keys in Ruby?

Use curly braces with strings as keys and hash rockets, like: { "name" => "Alice", "age" => 30 }.

intermediate

What is the difference between symbol keys and string keys in Ruby hashes?

Symbol keys are immutable and often faster, while string keys are mutable. Symbols are written without quotes and strings with quotes.

intermediate

Show an example of a Ruby hash mixing symbol and string keys.

Example: { name: "Alice", "age" => 30 }. You can mix keys but be careful when accessing values.

Which of these is a valid Ruby hash with symbol keys?

A { name: "Bob", city: "NY" }

B { "name" => "Bob", "city" => "NY" }

C [ name: "Bob", city: "NY" ]

D ( name: "Bob", city: "NY" )

Option A uses symbol keys with colons inside curly braces, which is the correct syntax for symbol-key hashes.

How do you access the value for key :name in hash { name: "Eve" }?

A hash["name"]

B hash[:name]

C hash.name

D hash->name

You access symbol keys using the symbol itself inside square brackets, like hash[:name].

Which symbol key is equivalent to the string key "age" in a Ruby hash?

A :age

B "age"

C age

D age:

The symbol :age is a different type from the string "age" but often used as a key in hashes.

What happens if you mix symbol and string keys in a Ruby hash?

A They are treated as the same key

B The string key overrides the symbol key

C They are treated as different keys

D Ruby throws an error

Symbol and string keys are different objects, so they are treated as different keys in a hash.

Which syntax creates a hash with string keys?

A { color: "red", size: "M" }

B ( color: "red", size: "M" )

C [ "color" => "red", "size" => "M" ]

D { "color" => "red", "size" => "M" }

Using strings as keys requires the hash rocket => syntax inside curly braces.

Explain how to create a Ruby hash using symbol keys and how to access its values.

Think about keys without quotes and how you get values.

Describe the difference between using string keys and symbol keys in Ruby hashes.

Consider how keys look and behave.