Wolfram Language & System 11.0 (2016)|Legacy Documentation

This is documentation for an earlier version of the Wolfram Language.View current documentation (Version 11.2)

Once

Once[expr]
evaluates expr once in each Wolfram Language session, always returning the result from the first evaluation.

DetailsDetails

  • When first used in a session, Once[expr] evaluates expr and returns the result.
  • Subsequent uses of Once[expr] do not evaluate expr again, and return the result from when expr was first evaluated.
  • Once has attribute HoldFirst.
  • Unset[Once[expr]] removes any stored value for Once[expr].
Introduced in 2016
(11.0)