change FIRST/LAST to select nothing on empty sequences, closes #4

CHANGES.md

@@ -1,3 +1,7 @@
+## 0.5.6
+* Add multi-path implementation
+* change FIRST/LAST to select nothing on an empty sequence
+
 ## 0.5.5
 * Change filterer to accept a selector (that acts like selected? to determine whether or not to select value)
 

src/clj/com/rpl/specter.clj

@@ -113,9 +113,9 @@
 
 (def VAL (->ValCollect))
 
-(def LAST (->LastStructurePath))
+(def LAST (->PosStructurePath last set-last))
 
-(def FIRST (->FirstStructurePath))
+(def FIRST (->PosStructurePath first set-first))
 
 (defn srange-dynamic [start-fn end-fn] (->SRangePath start-fn end-fn))
 

src/clj/com/rpl/specter/impl.clj

@@ -374,23 +374,17 @@
   (collect-val [this structure]
     structure))
 
-(deftype LastStructurePath [])
+(deftype PosStructurePath [getter setter])
 
 (extend-protocol StructurePath
-  LastStructurePath
+  PosStructurePath
   (select* [this structure next-fn]
-    (next-fn (last structure)))
+    (if-not (empty? structure)
+      (next-fn ((.getter this) structure))))
   (transform* [this structure next-fn]
-    (set-last structure (next-fn (last structure)))))
-
-(deftype FirstStructurePath [])
-
-(extend-protocol StructurePath
-  FirstStructurePath
-  (select* [this structure next-fn]
-    (next-fn (first structure)))
-  (transform* [this structure next-fn]
-    (set-first structure (next-fn (first structure)))))
+    (if (empty? structure)
+      structure
+      ((.setter this) structure (next-fn ((.getter this) structure))))))
 
 (deftype WalkerStructurePath [afn])