A Set is an unordered OCL collection with no duplicate elements; use it when you need a distinct group of values in an expression.
Create a Set
Use Set{...} and place the values between the braces.
Set{14, 22, 12, 53, 2, 11, 66}This expression creates a Set of integers. You can also create a Set of strings:
Set{'String', 'EmailAddress'}Duplicate values are removed
A Set retains each distinct value once. For example, this expression produces a Set containing 14, 22, and 53:
Set{14, 22, 14, 53, 22}Do not use a Set when repeated values have meaning. Use a Bag for a collection that can contain duplicates.
Use a Set with collection operations
You can use a Set as the source collection for OCL collection operations. For example, collect evaluates an expression for every integer in this Set:
Set{14, 22, 12, 53, 2, 11, 66}->collect(i | DoSomethingWithAnInt(i))Here, i is the current integer while the collect expression is evaluated. The called expression must be valid in the context where you use it.
The same pattern applies to strings:
Set{'String', 'EmailAddress'}->collect(s | DoSomethingWithAString(s))Choose the right collection type
| Use | When you need | Example |
|---|---|---|
| Set | Distinct values; element order is not defined. | Set{'New', 'Approved', 'Closed'}
|
| Bag | A collection in which duplicate values are retained. | Bag{'New', 'New', 'Closed'}
|
| Sequence | A collection whose order matters, such as a numeric range for iteration or numbering. | Sequence{0..20}
|
For example, use Sequence{0..20} rather than a Set when your expression depends on a number sequence in order. See Sequence for range syntax and ordered collections.
Convert an existing value or collection
Use asSet when you already have a value or collection and need a Set. Applied to a collection, asSet() removes duplicates; applied to a single value, it creates a Set containing that value.
For example:
someCollection->asSet()Work with Set values
Use difference to subtract the elements of one collection from another. For example, the result contains only 'a':
Set{'a', 'b', 'c', 'd'}->difference(Set{'b', 'c', 'd', 'e'})To obtain all currently existing instances of a classifier as a Set, use allInstances. To test whether a Set has no elements, use Empty.