I just came across ruby and noticed a difference between the behavior of 
Array.insert() and its documentation.

Method: http://www.ruby-doc.org/core/classes/Array.src/M002195.html

From the RDoc it seems that two arguments are mandatory, yet Array.insert() 
only raises an error if there is no argument passed at all.

Code snippet from Array.insert():

    if (argc == 1) return ary;
    if (argc < 1) {
        rb_raise(rb_eArgError, "wrong number of arguments (at least 1)");
    }

From my semantic understanding of an "insert" Method it should raise an error 
if called with less than two arguments, for silently returning the array can 
be irritating for beginners (Took me some time to figure it out).

best regards,
Markus Echterhoff