ruby String class: what is the "%" symbol a method?

Question

In the ruby (2.2.0) String class documentation, the very first INSTANCE method is the following:

str % arg → new_str

Format—Uses str as a format specification, and returns the result of applying it to arg. (...)

The first example provided is:

"%05d" % 123    #=> "00123"

and works as stated. Ok, but without a '.' the '%' can't be a method, can it?
And if it is not, what is instead (and why is listed under the 'instance methods'?)

Because it's an instance method. http://stackoverflow.com/a/3331974/438992 Ruby has a lot of syntatic sugar. Same way you can override other operators. — Dave Newton, Dec 26 '14 at 15:34

score 3 · Accepted Answer · answered Dec 26 '14 at 15:42

It's syntax sugar. You can call it with . if you want:

"%05d" % 123
# => "00123"

is equivalent to:

"%05d".% 123
# => "00123"

A similar example:

1 * 2 + 3
# => 5
(1.*(2)).+(3)
# => 5

The second form is valid, but we usually choose the first form as it's clearer.

ruby String class: what is the "%" symbol a method?

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