Use indexOf only when you must maintain an existing expression. It returns the position of an object in a sequence, but its zero-based result does not match the one-based indexing used by at.

Signature

indexOf(object : T) : Integer

indexOf searches the sequence in self for object and returns its position.

Return value

Result	Meaning
0 or greater	The zero-based position of the object in the sequence. 0 is the first element.
-1	The object is not present in the sequence.

For example, if a sequence contains the cars Toyota and Volvo, in that order, finding Toyota with indexOf returns 0. Finding a car that is not in the sequence returns -1.

Important: index base does not match at

indexOf is zero-based, while at is one-based. Do not pass an indexOf result directly to at.

For example, when indexOf(Toyota) returns 0, that value identifies the first item under zero-based indexing. The at operator uses one-based indexing, where the first item is position 1. This difference can produce an off-by-one result.

Use the explicit zero-based operators

For new OCL expressions, use indexOf0 together with at0. Both operators use zero-based indexing, so their results and input values align.

1. Find the position with indexOf0.
2. Check whether the result is -1 before using it as an index.
3. Retrieve an item with at0 when you need to use that position.

Example: if indexOf0(Toyota) returns 0, at0(0) refers to the first item in the sequence.

Handle objects that are not found

A result of -1 means that the search did not find the object. Do not use -1 as an index. Test the result first when the object may be absent.

Use isEmpty when you need to test whether a collection contains any elements before performing collection work.

See also

• Documentation:OCLOperators indexOf0
• Documentation:OCLOperators at0
• Documentation:Examples on collection operators
• Documentation:OCL General Operators