std.functional.memoize: Ability to clear the cache

[dlangBugzillaToGithub]

aurelien.fredouelle+dlang (@AurelC2G) reported this on 2019-05-11T08:51:53Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=19859

Description

Other common implementations of memoize usually allow to reset the cache. For example, this is quite common in python:

@memoize
def square (x):
  return x*x

square(2)
square(3)

square.cache.clear()

It would be helpful if we could accomplish the same with std.functional.memoize.

[dlangBugzillaToGithub]

aurelien.fredouelle+dlang commented on 2019-05-12T12:01:54Z

Just tried implementing this by making memoize a struct with a static opCall: https://github.com/dlang/phobos/compare/master...AurelC2G:19859-memoize-cache-clear

However I ran into bug #18289, so this doesn't work as-is.

Any suggestions?