standard library: 'max' and 'min' functions reimplemented to avoid unnecessary null checks

(as proposed for minBy/maxBy in https://github.com/JetBrains/kotlin/pull/324)

libraries/tools/kotlin-stdlib-gen/src/templates/Commons.kt

@@ -416,44 +416,6 @@ fun commons(): ArrayList<GenericFunction> {
         }
     }
 
-    templates add f("min()") {
-        doc = "Returns the smallest element or null if there are no elements"
-        returns("T?")
-        absentFor(PrimitiveType.Boolean, PrimitiveType.Char)//currently there are no sane way to compare Char? with something (KT-4251)
-        typeParam("T: Comparable<T>")
-        isInline = false
-        body {
-            """
-                var min: T? = null
-                for (e in this) {
-                    if (min == null || min!! > e) {
-                       min = e
-                    }
-                }
-                return min
-            """
-        }
-    }
-
-    templates add f("max()") {
-        doc = "Returns the largest element or null if there are no elements"
-        returns("T?")
-        absentFor(PrimitiveType.Boolean, PrimitiveType.Char)//currently there are no sane way to compare Char? with something (KT-4251)
-        typeParam("T: Comparable<T>")
-        isInline = false
-        body {
-            """
-                var max: T? = null
-                for (e in this) {
-                    if (max == null || max!! < e) {
-                       max = e
-                    }
-                }
-                return max
-            """
-        }
-    }
-
     templates add f("appendString(buffer: Appendable, separator: String = \", \", prefix: String =\"\", postfix: String = \"\", limit: Int = -1, truncated: String = \"...\")") {
         isInline = false
         doc =

libraries/tools/kotlin-stdlib-gen/src/templates/Iterables.kt

@@ -146,6 +146,76 @@ fun iterables(): ArrayList<GenericFunction> {
         }
     }
 
+    templates add f("min()") {
+        doc = "Returns the smallest element or null if there are no elements"
+        returns("T?")
+        absentFor(PrimitiveType.Boolean, PrimitiveType.Char)//currently there are no sane way to compare Char? with something (KT-4251)
+        typeParam("T: Comparable<T>")
+        isInline = false
+        Iterables.body {
+            """
+                val iterator = iterator()
+                if (!iterator.hasNext()) return null
+                
+                var min = iterator.next()
+                while (iterator.hasNext()) {
+                    val e = iterator.next()
+                    if (min > e) min = e
+                }
+                return min
+            """
+        }
+        listOf(Arrays, PrimitiveArrays).forEach {
+            it.body {
+                """
+                if (isEmpty()) return null
+                
+                var min = this[0]
+                for (i in 1..lastIndex) {
+                    val e = this[i]
+                    if (min > e) min = e
+                }
+                return min
+            """
+            }
+        }
+    }
+
+    templates add f("max()") {
+        doc = "Returns the largest element or null if there are no elements"
+        returns("T?")
+        absentFor(PrimitiveType.Boolean, PrimitiveType.Char)//currently there are no sane way to compare Char? with something (KT-4251)
+        typeParam("T: Comparable<T>")
+        isInline = false
+        Iterables.body {
+            """
+                val iterator = iterator()
+                if (!iterator.hasNext()) return null
+                
+                var max = iterator.next()
+                while (iterator.hasNext()) {
+                    val e = iterator.next()
+                    if (max < e) max = e
+                }
+                return max
+            """
+        }
+        listOf(Arrays, PrimitiveArrays).forEach {
+            it.body {
+                """
+                if (isEmpty()) return null
+                
+                var max = this[0]
+                for (i in 1..lastIndex) {
+                    val e = this[i]
+                    if (max < e) max = e
+                }
+                return max
+            """
+            }
+        }
+    }
+
     templates add f("minBy(f: (T) -> R)") {
         doc = "Returns the first element yielding the smallest value of the given function or null if there are no elements"
         typeParam("R: Comparable<R>")

libraries/tools/kotlin-stdlib-gen/src/templates/Iterators.kt

@@ -132,6 +132,44 @@ fun iterators(): List<GenericFunction> {
         }
     }
 
+    templates add f("min()") {
+        doc = "Returns the smallest element or null if there are no elements"
+        returns("T?")
+        typeParam("T: Comparable<T>")
+        isInline = false
+        body {
+            """
+                if (!hasNext()) return null
+                
+                var min = next()
+                while (hasNext()) {
+                    val e = next()
+                    if (min > e) min = e
+                }
+                return min
+            """
+        }
+    }
+
+    templates add f("max()") {
+        doc = "Returns the largest element or null if there are no elements"
+        returns("T?")
+        typeParam("T: Comparable<T>")
+        isInline = false
+        body {
+            """
+                if (!hasNext()) return null
+                
+                var max = next()
+                while (hasNext()) {
+                    val e = next()
+                    if (max < e) max = e
+                }
+                return max
+            """
+        }
+    }
+    
     templates add f("minBy(f: (T) -> R)") {
         doc = "Returns the first element yielding the smallest value of the given function or null if there are no elements"
         typeParam("R: Comparable<R>")