What are parentheses in the Ruby programming language?

Parentheses in Ruby can be used for different purposes depending on the context:

• Calling a method with arguments. method_name(argument1, argument2)
• Accessing an element of an array or hash. array[index], hash[key]
• Defining an array or hash. [element1, element2], {key1 => value1, key2 => value2}
• Grouping expressions to change the order of execution. (expression1 + expression2) * 3
• Defining code blocks (for single lines). Although for multi-line blocks, do...end is more common, parentheses () can also be used. array.each { |item| puts item }

# Calling a method with arguments
puts("Hello, world!")

# Accessing an array element
my_array = [1, 2, 3]
puts my_array[1] # Will output 2

# Accessing a hash element
my_hash = { "a" => 1, "b" => 2 }
puts my_hash["a"] # Will output 1

# Defining an array
another_array = [4, 5, 6]

# Defining a hash
another_hash = { "c" => 3, "d" => 4 }

# Grouping expressions
result = (5 + 3) * 2 # The result will be 16, not 11

# Code block (single line)
[1, 2, 3].each { |n| puts n * 2 }