Convert

In Ruby a custom method can convert types—but this is rarely needed. We instead use built-in methods to convert common types like strings, arrays and hashes.

When possible, built-in methods are a good choice. They cover many edge cases, so you may need to make fewer changes. And they are fast to test and deploy.

String, array

A string can be converted to an array of characters with the split method. Here, we use a string that has 4 characters. After splitting, we have an array of 4 values.

# Input string has four characters.
value = "test"

# Split on an empty string delimiter.
elements = value.split ""

# Display result.
puts elements.length
puts elements
4
t
e
s
t

Array, string

The join method combines elements of an array together into a new string. This is an ideal way to convert an array into a string.

# The input array has three characters.
values = ["a", "b", "c"]

# Call join on the array.
result = values.join
puts result
abc

Hash

This example is somewhat more complex. It introduces a hash, and then converts the keys and values into arrays and strings. So we get a string of all the keys, and one of the values.

# An example hash.
hash = {"a" => 1, "b" => 2, "c" => 3}

# Convert keys into a string.
result = hash.keys.join
print "KEYS: ", result, "\n"

# Convert values into a string.
result = hash.values.join
print "VALUES: ", result, "\n"

# Convert entire hash into an array.
elements = hash.to_a
print "ARRAY LENGTH: ", elements.length, "\n"
print "ARRAY       : ", elements, "\n"
KEYS: abc
VALUES: 123
ARRAY LENGTH: 3
ARRAY       : [["a", 1], ["b", 2], ["c", 3]]

Number, string

Numbers can be converted into Strings with the String method. This receives a numeric variable and returns a String. It works on integers and floating-point values.

number = 1234

# Convert to String with String method.
value = String(number)

# Test String value.
if value == "1234"
    puts true
end
true

String, integer

Often a program reads in a file that contains numbers, or a use renters a number stored as a string. We convert these strings with the Integer built-in method.

value = "1234"

# Convert String to Integer.
number = Integer(value)

# Test Integer for correctness.
if number == 1234
    puts true
end
true

Invalid string

We encounter an ArgumentError if we try to convert a non-numeric String to an Integer. We can work around this problem with a begin and raise block.

# Will not work.
value = "x"
number = Integer(value)
file.rb:3:in `Integer': invalid value for Integer(): "x" (ArgumentError)
begin
    # This is not a valid number string.
    value = "x"
    number = Integer(value)
rescue
    # An error is raised.
    puts "Invalid number"
end
Invalid number

Converting types is an uninteresting task, but it is necessary. With this knowledge, we can focus more on core program design. And this focus leads to better, higher-quality programs.