indexOf0 finds the zero-based position of an object in a sequence, for you when you need an index that can be used consistently with the zero-based at0 operator.

Syntax

sequence->indexOf0(object)

indexOf0 has the following signature:

indexOf0(object : T) : Integer

Return value

indexOf0 returns the position of object in self, using zero-based indexing. The first object has index 0.

Situation	Result
The object is at the first position in the sequence	0
The object is at the third position in the sequence	2
The object does not exist in the sequence	-1

Example

Given a sequence named cars in which toyota is the first object:

cars->indexOf0(toyota)

The expression returns 0.

If ford is not in cars:

cars->indexOf0(ford)

The expression returns -1.

Use the result with at0

Use indexOf0 when you intend to use the returned index with at0. Check for -1 before attempting to retrieve an object, because -1 means that no matching object was found.

let index : Integer = cars->indexOf0(toyota) in
if index >= 0 then
  cars->at0(index)
else
  null
endif

This expression returns the object at the found zero-based index, or null when toyota is not in the sequence.

indexOf0 compared with indexOf

indexOf also returns a zero-based index in MDriven, although its name does not make that convention clear. Prefer indexOf0 together with at0 so that the zero-based indexing is explicit. This avoids mixing it with at, which uses one-based indexing.

See also

• Documentation:OCLOperators indexOf
• Documentation:OCL General Operators
• Documentation:OCLOperators isEmpty