Add function to get the segment from a static variable

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file. This change log follows the conventions of [keepachangelog.com](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Added
+- New function to allow getting the backing memory segment of a `coffi.ffi.StaticVariable`, to replace the `Addressable` implementation lost in the migration to JDK 18
 
 ## [0.5.357] - 2022-07-07
 ### Removed

src/clj/coffi/ffi.clj

@@ -19,6 +19,7 @@
     FunctionDescriptor
     MemoryAddress
     MemoryLayout
+    MemorySegment
     NativeSymbol
     SegmentAllocator)))
 
@@ -594,6 +595,14 @@
   [static-var f & args]
   (freset! static-var (apply f @static-var args)))
 
+(defn static-variable-segment
+  "Gets the backing [[MemorySegment]] from `static-var`.
+
+  This is primarily useful when you need to pass the static variable's address
+  to a native function which takes an [[Addressable]]."
+  ^MemorySegment [static-var]
+  (.-seg ^StaticVariable static-var))
+
 (defn static-variable
   "Constructs a reference to a mutable value stored in `symbol-or-addr`.