indexOf ( object : T ) : Integer

Returns the position of object in sequence self.

Expression	Result
Sequence{'a', 'b'}->indexOf('a')	0

The zero-based index of an object in the collection is possibly -1 if nonexistent.

(note that probably the specification says that this should be 1-based and not 0-based as it is. This makes it a confusing to use the at(int)-operator that IS 1 based.

We have introduced a IndexOf0:int that explicitly is zero based to better sit with the explicit zero based at0(int))

We recommend you use IndexOf0 and at0 operators over IndexOf and at