How to write a BOOL predicate in Core Data?

Swift 3

let predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(value: true))

---

In Swift 3 you should use NSNumber(value: true).

Using NSNumber(booleanLiteral: true) and in general any literal initialiser directly is discouraged and for example SwiftLint (v. 0.16.1) will generate warning for usage ExpressibleBy...Literal initialiser directly:

Compiler Protocol Init Violation: The initializers declared in compiler protocols such as ExpressibleByArrayLiteral shouldn't be called directly. (compiler_protocol_init)

Swift 4.0

let predicate = NSPredicate(format: "boolAttribute == %@", NSNumber(value: true))

From Predicate Programming Guide:

You specify and test for equality of Boolean values as illustrated in the following examples:

NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"anAttribute == %@", [NSNumber numberWithBool:aBool]];
NSPredicate *testForTrue = [NSPredicate predicateWithFormat:@"anAttribute == YES"];

You can also check out the Predicate Format String Syntax.

Don't convert to NSNumber, nor use double "=="

More appropriate for Swift >= 4:

NSPredicate(format: "boolAttribute = %d", true)

Note: "true" in this example is a Bool (a Struct)