What's the Difference Between String#to_i and Kernel#Integer Methods in Ruby?

Ruby to_i() vs. Integer()

The Ruby String#to_i and Kernel#Integer methods differ in terms of how they convert strings and nil:

to_i() Integer()
only interprets leading characters as numbers in a string, and ignores characters beyond the end of a valid number. throws an ArgumentError if string is not strictly numeric.
returns 0 if there's no valid number found at the start of a string.
does not automatically convert strings with radix indicators (such as 0, 0b, and 0x), instead it requires explicitly passing the integer base (between 2 and 36) to output the integer in a different numeral system (e.g. "100".to_i(2)). automatically converts strings with radix indicators (such as 0, 0b, and 0x), and also accepts base number (between 2 and 36) to be passed in optionally as an argument.
returns 0 for nil. throws TypeError for nil.

For example:

value value.to_i Integer(value)
"50" 50 50
"50 foo" 50 ArgumentError
"50 foo 100" 50 ArgumentError
"50.123" 50 ArgumentError
"foo bar 50" 0 ArgumentError
"foo bar" 0 ArgumentError
"0b100000000" 0 256
"0400" 400 256
"0x100" 0 256
nil 0 TypeError

For non-string values, Integer method uses to_int first and then to_i for conversion. Therefore, they yield the same result for non-string values.


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