added must navigator

CHANGES.md

@@ -1,3 +1,6 @@
+## 0.10.1 (unreleased)
+* Added `must` navigator
+
 ## 0.10.0
 * Make codebase bootstrap cljs compatible
 * Remove usage of reducers in cljs version in favor of transducers (thanks @StephenRudolph)

VERSION

@@ -1 +1 @@
-0.10.0
+0.10.1-SNAPSHOT

src/clj/com/rpl/specter.cljx

@@ -269,13 +269,28 @@
                                       next-val))
                             structure)))))
 
-(defpath keypath [key]
+(defpath
+  ^{:doc "Navigates to the specified key, navigating to nil if it does not exist."}
+  keypath
+  [key]
   (select* [this structure next-fn]
     (next-fn (get structure key)))
   (transform* [this structure next-fn]
     (assoc structure key (next-fn (get structure key)))
     ))
 
+(defpath
+  ^{:doc "Navigates to the key only if it exists in the map."}
+  must
+  [k]
+  (select* [this structure next-fn]
+    (next-fn (get structure k)))
+  (transform* [this structure next-fn]
+   (if (contains? structure k)
+     (assoc structure k (next-fn (get structure k)))
+     structure
+     )))
+
 (defpath view [afn]
   (select* [this structure next-fn]
     (next-fn (afn structure)))

test/com/rpl/specter/core_test.cljx

@@ -244,6 +244,19 @@
        (s/transform (s/view afn) identity i)
        )))
 
+(defspec must-test
+  (for-all+
+    [k1 gen/int
+     k2 (gen/such-that #(not= k1 %) gen/int)
+     m (gen-map-with-keys gen/int gen/int k1)
+     op (gen/elements [inc dec])
+     ]
+    (let [m (dissoc m k2)]
+      (and (= (s/transform (s/must k1) op m)
+              (s/transform (s/keypath k1) op m))
+           (= (s/transform (s/must k2) op m) m)
+           ))))
+
 (defspec parser-test
   (for-all+
     [i gen/int
@@ -835,3 +848,4 @@
                (seq? l2) ; Transformed lists are only guaranteed to impelment ISeq
                (= q1 q2)
                (= (type q1) (type q2))))))
+