This causes weird, hard to debug issues when trying to modify Type::make. The same issue also affects NativeType::instance().

• I'm also not sure if there are any reference counting issues or garbage collection issues.
  I'm getting really weird output on a branch running ./test for https://github.com/TysonAndre/phan/compare/master...TysonAndre:optimize-uniontype-memory-static-issue-investigate?expand=1
  (Background : That branch is for speeding up phan and reduce the peak memory usage by a few percentage points)

Related bug on php.net: https://bugs.php.net/bug.php?id=73872
Also see https://3v4l.org/dt9bg

If there is a method that uses static variables, then there are multiple solutions

• Redeclare the method (or caching portion of this method) in each subclass and link to the bugs
• Use a protected/private static variable ( array mapping (possibly type) and fully qualified name to the signature)
  Or use a public static variable(array), redeclared in each subclass, accessed with static::$map