Add an address predicate

CHANGELOG.md

@@ -2,6 +2,9 @@
 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
+- An `address?` predicate
+
 ### Fixed
 - `nil` was not considered a null pointer
 - Primitive-serializing types fail to compile as arguments to downcall handles

src/clj/coffi/mem.clj

@@ -130,6 +130,13 @@
   [addr]
   (or (.equals (MemoryAddress/NULL) addr) (not addr)))
 
+(defn address?
+  "Checks if an object is a memory address.
+
+  `nil` is considered an address."
+  [addr]
+  (or (nil? addr) (instance? MemoryAddress addr)))
+
 (defn slice-global
   "Gets a slice of the global address space.