Hasher

The universal hash function used by Set and Dictionary.

Hasher can be used to map an arbitrary sequence of bytes to an integer hash value. You can feed data to the hasher using a series of calls to mutating combine methods. When you've finished feeding the hasher, the hash value can be retrieved by calling finalize():

  • var hasher = Hasher()
  • hasher.combine(23)
  • hasher.combine("Hello")
  • let hashValue = hasher.finalize()

Within the execution of a Swift program, Hasher guarantees that finalizing it will always produce the same hash value as long as it is fed the exact same sequence of bytes. However, the underlying hash algorithm is designed to exhibit avalanche effects: slight changes to the seed or the input byte sequence will typically produce drastic changes in the generated hash value.

Note: Do not save or otherwise reuse hash values across executions of your program. Hasher is usually randomly seeded, which means it will return different values on every new execution of your program. The hash algorithm implemented by Hasher may itself change between any two versions of the standard library.

Import
  • import Swift

Initializers

init()

Initialize a new hasher. The hasher uses a per-execution seed value that is set during process startup, usually from a high-quality random source.

Declaration

  • init()

Instance Methods

mutating func combine(_: UnsafeRawBufferPointer)

Feed the contents of buffer into this hasher, mixing it into the hasher state.

Declaration

mutating func combine<H>(_: H)

Feed value to this hasher, mixing its essential parts into the hasher state.

Declaration

  • mutating func combine<H>(_ value: H)
func finalize()

Finalize the hasher state and return the hash value.

Finalizing consumes the hasher: it is illegal to finalize a hasher you don't own, or to perform operations on a finalized hasher. (These may become compile-time errors in the future.)

Hash values are not guaranteed to be equal across different executions of your program. Do not save hash values to use during a future execution.

Declaration

  • func finalize() -> Int