<!--
{
  "availability" : [
    "iOS: 8.0.0 -",
    "iPadOS: 8.0.0 -",
    "macCatalyst: 13.0.0 -",
    "macOS: 10.10.0 -",
    "tvOS: 9.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 2.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "Swift",
  "identifier" : "/documentation/Swift/SetAlgebra/isStrictSubset(of:)",
  "metadataVersion" : "0.1.0",
  "role" : "Instance Method",
  "symbol" : {
    "kind" : "Instance Method",
    "modules" : [
      "Swift"
    ],
    "preciseIdentifier" : "s:s10SetAlgebraPsE14isStrictSubset2ofSbx_tF"
  },
  "title" : "isStrictSubset(of:)"
}
-->

# isStrictSubset(of:)

Returns a Boolean value that indicates whether this set is a strict
subset of the given set.

```
func isStrictSubset(of other: Self) -> Bool
```

## Parameters

`other`

A set of the same type as the current set.

## Return Value

`true` if the set is a strict subset of `other`; otherwise,
`false`.

## Discussion

Set *A* is a strict subset of another set *B* if every member of *A* is
also a member of *B* and *B* contains at least one element that is not a
member of *A*.

```
let employees: Set = ["Alicia", "Bethany", "Chris", "Diana", "Eric"]
let attendees: Set = ["Alicia", "Bethany", "Diana"]
print(attendees.isStrictSubset(of: employees))
// Prints "true"

// A set is never a strict subset of itself:
print(attendees.isStrictSubset(of: attendees))
// Prints "false"
```

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)