switched inferred checks for prevnext to index into results rather than allow supertype of result

Author: souma4

test/runtests.jl

@@ -242,10 +242,8 @@ const BT = BinaryTrees
     @inferred BT.insert!(tree, 3, 30)
     @inferred Nothing BT.minnode(tree)
     @inferred Nothing BT.maxnode(tree)
-    @inferred Tuple{Union{BT.AVLNode,Nothing},Union{BT.AVLNode,Nothing}} BT.prevnext(
-      tree,
-      2
-    )
+    @inferred Nothing BT.prevnext(tree, 2)[1]
+    @inferred Nothing BT.prevnext(tree, 2)[2]
     @inferred BT.prevnext(tree, nothing)
     @inferred Nothing BT.search(tree, 2)
     @inferred Nothing BT.search(tree, 1)
@@ -259,10 +257,10 @@ const BT = BinaryTrees
     @inferred BT.insert!(tree, 3)
     @inferred Nothing BT.minnode(tree)
     @inferred Nothing BT.maxnode(tree)
-    @inferred Tuple{Union{BT.AVLNode,Nothing},Union{BT.AVLNode,Nothing}} BT.prevnext(
-      tree,
-      2
-    )
+    @inferred Nothing BT.prevnext(tree, 2)[1]
+    @inferred Nothing BT.prevnext(tree, 2)[2]
+    @inferred BT.prevnext(tree, nothing)
+    @inferred Nothing BT.search(tree, 2)
     @inferred Nothing BT.search(tree, 2)
     @inferred Nothing BT.search(tree, 1)
     @inferred Nothing BT.search(tree, 3)
@@ -275,10 +273,9 @@ const BT = BinaryTrees
     @inferred BT.insert!(tree, "key3", 3)
     @inferred Nothing BT.minnode(tree)
     @inferred Nothing BT.maxnode(tree)
-    @inferred Tuple{Union{BT.AVLNode,Nothing},Union{BT.AVLNode,Nothing}} BT.prevnext(
-      tree,
-      "key2"
-    )
+    @inferred Nothing BT.prevnext(tree, "key2")[1]
+    @inferred Nothing BT.prevnext(tree, "key2")[2]
+    @inferred BT.prevnext(tree, nothing)
     @inferred Nothing BT.search(tree, "key2")
     @inferred Nothing BT.search(tree, "key1")
     @inferred Nothing BT.search(tree, "key3")
@@ -291,10 +288,9 @@ const BT = BinaryTrees
     @inferred BT.insert!(tree, (1, 0, 0), 3)
     @inferred Nothing BT.minnode(tree)
     @inferred Nothing BT.maxnode(tree)
-    @inferred Tuple{Union{BT.AVLNode,Nothing},Union{BT.AVLNode,Nothing}} BT.prevnext(
-      tree,
-      (0, 1, 0)
-    )
+    @inferred Nothing BT.prevnext(tree, (0, 1, 0))[1]
+    @inferred Nothing BT.prevnext(tree, (0, 1, 0))[2]
+    @inferred BT.prevnext(tree, nothing)
     @inferred Nothing BT.search(tree, (0, 1, 0))
     @inferred Nothing BT.search(tree, (0, 0, 1))
     @inferred Nothing BT.search(tree, (1, 0, 0))