[SPARK-4397][Core] Reorganize 'implicit's to improve the API convenience

core/src/main/scala/org/apache/spark/Accumulators.scala

@@ -244,6 +244,36 @@ trait AccumulatorParam[T] extends AccumulableParam[T, T] {
   }
 }
 
+object AccumulatorParam {
+
+  // The following implicit objects were in SparkContext before 1.2 and users had to
+  // `import SparkContext._` to enable them. Now we move them here to make the compiler find
+  // them automatically. However, as there are duplicate codes in SparkContext for backward
+  // compatibility, please update them accordingly if you modify the following implicit objects.
+
+  implicit object DoubleAccumulatorParam extends AccumulatorParam[Double] {
+    def addInPlace(t1: Double, t2: Double): Double = t1 + t2
+    def zero(initialValue: Double) = 0.0
+  }
+
+  implicit object IntAccumulatorParam extends AccumulatorParam[Int] {
+    def addInPlace(t1: Int, t2: Int): Int = t1 + t2
+    def zero(initialValue: Int) = 0
+  }
+
+  implicit object LongAccumulatorParam extends AccumulatorParam[Long] {
+    def addInPlace(t1: Long, t2: Long) = t1 + t2
+    def zero(initialValue: Long) = 0L
+  }
+
+  implicit object FloatAccumulatorParam extends AccumulatorParam[Float] {
+    def addInPlace(t1: Float, t2: Float) = t1 + t2
+    def zero(initialValue: Float) = 0f
+  }
+
+  // TODO: Add AccumulatorParams for other types, e.g. lists and strings
+}
+
 // TODO: The multi-thread support in accumulators is kind of lame; check
 // if there's a more intuitive way of doing it right
 private object Accumulators {

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1427,47 +1427,74 @@ object SparkContext extends Logging {
 
   private[spark] val DRIVER_IDENTIFIER = "<driver>"
 
-  implicit object DoubleAccumulatorParam extends AccumulatorParam[Double] {
+  // The following deprecated objects have already been copied to `object AccumulatorParam` to
+  // make the compiler find them automatically. They are duplicate codes only for backward
+  // compatibility, please update `object AccumulatorParam` accordingly if you plan to modify the
+  // following ones.
+
+  @deprecated("Replaced by implicit objects in AccumulatorParam. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  object DoubleAccumulatorParam extends AccumulatorParam[Double] {
     def addInPlace(t1: Double, t2: Double): Double = t1 + t2
     def zero(initialValue: Double) = 0.0
   }
 
-  implicit object IntAccumulatorParam extends AccumulatorParam[Int] {
+  @deprecated("Replaced by implicit objects in AccumulatorParam. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  object IntAccumulatorParam extends AccumulatorParam[Int] {
     def addInPlace(t1: Int, t2: Int): Int = t1 + t2
     def zero(initialValue: Int) = 0
   }
 
-  implicit object LongAccumulatorParam extends AccumulatorParam[Long] {
+  @deprecated("Replaced by implicit objects in AccumulatorParam. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  object LongAccumulatorParam extends AccumulatorParam[Long] {
     def addInPlace(t1: Long, t2: Long) = t1 + t2
     def zero(initialValue: Long) = 0L
   }
 
-  implicit object FloatAccumulatorParam extends AccumulatorParam[Float] {
+  @deprecated("Replaced by implicit objects in AccumulatorParam. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  object FloatAccumulatorParam extends AccumulatorParam[Float] {
     def addInPlace(t1: Float, t2: Float) = t1 + t2
     def zero(initialValue: Float) = 0f
   }
 
-  // TODO: Add AccumulatorParams for other types, e.g. lists and strings
+  // The following deprecated functions have already been moved to `object RDD` to
+  // make the compiler find them automatically. They are still kept here for backward compatibility
+  // and just call the corresponding functions in `object RDD`.
 
-  implicit def rddToPairRDDFunctions[K, V](rdd: RDD[(K, V)])
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def rddToPairRDDFunctions[K, V](rdd: RDD[(K, V)])
       (implicit kt: ClassTag[K], vt: ClassTag[V], ord: Ordering[K] = null) = {
-    new PairRDDFunctions(rdd)
+    RDD.rddToPairRDDFunctions(rdd)
   }
 
-  implicit def rddToAsyncRDDActions[T: ClassTag](rdd: RDD[T]) = new AsyncRDDActions(rdd)
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def rddToAsyncRDDActions[T: ClassTag](rdd: RDD[T]) = RDD.rddToAsyncRDDActions(rdd)
 
-  implicit def rddToSequenceFileRDDFunctions[K <% Writable: ClassTag, V <% Writable: ClassTag](
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def rddToSequenceFileRDDFunctions[K <% Writable: ClassTag, V <% Writable: ClassTag](
       rdd: RDD[(K, V)]) =
-    new SequenceFileRDDFunctions(rdd)
+    RDD.rddToSequenceFileRDDFunctions(rdd)
 
-  implicit def rddToOrderedRDDFunctions[K : Ordering : ClassTag, V: ClassTag](
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def rddToOrderedRDDFunctions[K : Ordering : ClassTag, V: ClassTag](
       rdd: RDD[(K, V)]) =
-    new OrderedRDDFunctions[K, V, (K, V)](rdd)
+    RDD.rddToOrderedRDDFunctions(rdd)
 
-  implicit def doubleRDDToDoubleRDDFunctions(rdd: RDD[Double]) = new DoubleRDDFunctions(rdd)
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def doubleRDDToDoubleRDDFunctions(rdd: RDD[Double]) = RDD.doubleRDDToDoubleRDDFunctions(rdd)
 
-  implicit def numericRDDToDoubleRDDFunctions[T](rdd: RDD[T])(implicit num: Numeric[T]) =
-    new DoubleRDDFunctions(rdd.map(x => num.toDouble(x)))
+  @deprecated("Replaced by implicit functions in the RDD companion object. This is " +
+    "kept here only for backward compatibility.", "1.2.0")
+  def numericRDDToDoubleRDDFunctions[T](rdd: RDD[T])(implicit num: Numeric[T]) =
+    RDD.numericRDDToDoubleRDDFunctions(rdd)
 
   // Implicit conversions to common Writable types, for saveAsSequenceFile
 
@@ -1493,40 +1520,49 @@ object SparkContext extends Logging {
         arr.map(x => anyToWritable(x)).toArray)
   }
 
-  // Helper objects for converting common types to Writable
-  private def simpleWritableConverter[T, W <: Writable: ClassTag](convert: W => T)
-      : WritableConverter[T] = {
-    val wClass = classTag[W].runtimeClass.asInstanceOf[Class[W]]
-    new WritableConverter[T](_ => wClass, x => convert(x.asInstanceOf[W]))
-  }
+  // The following deprecated functions have already been moved to `object WritableConverter` to
+  // make the compiler find them automatically. They are still kept here for backward compatibility
+  // and just call the corresponding functions in `object WritableConverter`.
 
-  implicit def intWritableConverter(): WritableConverter[Int] =
-    simpleWritableConverter[Int, IntWritable](_.get)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def intWritableConverter(): WritableConverter[Int] =
+    WritableConverter.intWritableConverter()
 
-  implicit def longWritableConverter(): WritableConverter[Long] =
-    simpleWritableConverter[Long, LongWritable](_.get)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def longWritableConverter(): WritableConverter[Long] =
+    WritableConverter.longWritableConverter()
 
-  implicit def doubleWritableConverter(): WritableConverter[Double] =
-    simpleWritableConverter[Double, DoubleWritable](_.get)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def doubleWritableConverter(): WritableConverter[Double] =
+    WritableConverter.doubleWritableConverter()
 
-  implicit def floatWritableConverter(): WritableConverter[Float] =
-    simpleWritableConverter[Float, FloatWritable](_.get)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def floatWritableConverter(): WritableConverter[Float] =
+    WritableConverter.floatWritableConverter()
 
-  implicit def booleanWritableConverter(): WritableConverter[Boolean] =
-    simpleWritableConverter[Boolean, BooleanWritable](_.get)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def booleanWritableConverter(): WritableConverter[Boolean] =
+    WritableConverter.booleanWritableConverter()
 
-  implicit def bytesWritableConverter(): WritableConverter[Array[Byte]] = {
-    simpleWritableConverter[Array[Byte], BytesWritable](bw =>
-      // getBytes method returns array which is longer then data to be returned
-      Arrays.copyOfRange(bw.getBytes, 0, bw.getLength)
-    )
-  }
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def bytesWritableConverter(): WritableConverter[Array[Byte]] =
+    WritableConverter.bytesWritableConverter()
 
-  implicit def stringWritableConverter(): WritableConverter[String] =
-    simpleWritableConverter[String, Text](_.toString)
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def stringWritableConverter(): WritableConverter[String] =
+    WritableConverter.stringWritableConverter()
 
-  implicit def writableWritableConverter[T <: Writable]() =
-    new WritableConverter[T](_.runtimeClass.asInstanceOf[Class[T]], _.asInstanceOf[T])
+  @deprecated("Replaced by implicit functions in WritableConverter. This is kept here only for " +
+    "backward compatibility.", "1.2.0")
+  def writableWritableConverter[T <: Writable]() =
+    WritableConverter.writableWritableConverter()
 
   /**
    * Find the JAR from which a given class was loaded, to make it easy for users to pass
@@ -1750,3 +1786,46 @@ private[spark] class WritableConverter[T](
     val writableClass: ClassTag[T] => Class[_ <: Writable],
     val convert: Writable => T)
   extends Serializable
+
+object WritableConverter {
+
+  // Helper objects for converting common types to Writable
+  private[spark] def simpleWritableConverter[T, W <: Writable: ClassTag](convert: W => T)
+  : WritableConverter[T] = {
+    val wClass = classTag[W].runtimeClass.asInstanceOf[Class[W]]
+    new WritableConverter[T](_ => wClass, x => convert(x.asInstanceOf[W]))
+  }
+
+  // The following implicit functions were in SparkContext before 1.2 and users had to
+  // `import SparkContext._` to enable them. Now we move them here to make the compiler find
+  // them automatically. However, we still keep the old functions in SparkContext for backward
+  // compatibility and forward to the following functions directly.
+
+  implicit def intWritableConverter(): WritableConverter[Int] =
+    simpleWritableConverter[Int, IntWritable](_.get)
+
+  implicit def longWritableConverter(): WritableConverter[Long] =
+    simpleWritableConverter[Long, LongWritable](_.get)
+
+  implicit def doubleWritableConverter(): WritableConverter[Double] =
+    simpleWritableConverter[Double, DoubleWritable](_.get)
+
+  implicit def floatWritableConverter(): WritableConverter[Float] =
+    simpleWritableConverter[Float, FloatWritable](_.get)
+
+  implicit def booleanWritableConverter(): WritableConverter[Boolean] =
+    simpleWritableConverter[Boolean, BooleanWritable](_.get)
+
+  implicit def bytesWritableConverter(): WritableConverter[Array[Byte]] = {
+    simpleWritableConverter[Array[Byte], BytesWritable](bw =>
+      // getBytes method returns array which is longer then data to be returned
+      Arrays.copyOfRange(bw.getBytes, 0, bw.getLength)
+    )
+  }
+
+  implicit def stringWritableConverter(): WritableConverter[String] =
+    simpleWritableConverter[String, Text](_.toString)
+
+  implicit def writableWritableConverter[T <: Writable]() =
+    new WritableConverter[T](_.runtimeClass.asInstanceOf[Class[T]], _.asInstanceOf[T])
+}

core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala

@@ -32,13 +32,13 @@ import org.apache.hadoop.mapreduce.{OutputFormat => NewOutputFormat}
 
 import org.apache.spark.{HashPartitioner, Partitioner}
 import org.apache.spark.Partitioner._
-import org.apache.spark.SparkContext.rddToPairRDDFunctions
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.api.java.JavaSparkContext.fakeClassTag
 import org.apache.spark.api.java.JavaUtils.mapAsSerializableJavaMap
 import org.apache.spark.api.java.function.{Function => JFunction, Function2 => JFunction2, PairFunction}
 import org.apache.spark.partial.{BoundedDouble, PartialResult}
 import org.apache.spark.rdd.{OrderedRDDFunctions, RDD}
+import org.apache.spark.rdd.RDD.rddToPairRDDFunctions
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.util.Utils
 

core/src/main/scala/org/apache/spark/api/java/JavaSparkContext.scala

@@ -33,7 +33,7 @@ import org.apache.hadoop.mapred.{InputFormat, JobConf}
 import org.apache.hadoop.mapreduce.{InputFormat => NewInputFormat}
 
 import org.apache.spark._
-import org.apache.spark.SparkContext._
+import org.apache.spark.AccumulatorParam._
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.api.java.JavaSparkContext.fakeClassTag
 import org.apache.spark.broadcast.Broadcast

core/src/main/scala/org/apache/spark/rdd/RDD.scala

@@ -21,13 +21,15 @@ import java.util.{Properties, Random}
 
 import scala.collection.{mutable, Map}
 import scala.collection.mutable.ArrayBuffer
+import scala.language.implicitConversions
 import scala.reflect.{classTag, ClassTag}
 
 import com.clearspring.analytics.stream.cardinality.HyperLogLogPlus
 import org.apache.hadoop.io.BytesWritable
 import org.apache.hadoop.io.compress.CompressionCodec
 import org.apache.hadoop.io.NullWritable
 import org.apache.hadoop.io.Text
+import org.apache.hadoop.io.Writable
 import org.apache.hadoop.mapred.TextOutputFormat
 
 import org.apache.spark._
@@ -1383,3 +1385,31 @@ abstract class RDD[T: ClassTag](
     new JavaRDD(this)(elementClassTag)
   }
 }
+
+object RDD {
+
+  // The following implicit functions were in SparkContext before 1.2 and users had to
+  // `import SparkContext._` to enable them. Now we move them here to make the compiler find
+  // them automatically. However, we still keep the old functions in SparkContext for backward
+  // compatibility and forward to the following functions directly.
+
+  implicit def rddToPairRDDFunctions[K, V](rdd: RDD[(K, V)])
+      (implicit kt: ClassTag[K], vt: ClassTag[V], ord: Ordering[K] = null) = {
+    new PairRDDFunctions(rdd)
+  }
+
+  implicit def rddToAsyncRDDActions[T: ClassTag](rdd: RDD[T]) = new AsyncRDDActions(rdd)
+
+  implicit def rddToSequenceFileRDDFunctions[K <% Writable: ClassTag, V <% Writable: ClassTag](
+      rdd: RDD[(K, V)]) =
+    new SequenceFileRDDFunctions(rdd)
+
+  implicit def rddToOrderedRDDFunctions[K : Ordering : ClassTag, V: ClassTag](
+      rdd: RDD[(K, V)]) =
+    new OrderedRDDFunctions[K, V, (K, V)](rdd)
+
+  implicit def doubleRDDToDoubleRDDFunctions(rdd: RDD[Double]) = new DoubleRDDFunctions(rdd)
+
+  implicit def numericRDDToDoubleRDDFunctions[T](rdd: RDD[T])(implicit num: Numeric[T]) =
+    new DoubleRDDFunctions(rdd.map(x => num.toDouble(x)))
+}

core/src/test/scala/org/apache/spark/SparkContextSuite.scala

@@ -29,7 +29,7 @@ class SparkContextSuite extends FunSuite {
     bytesWritable.set(inputArray, 0, 10)
     bytesWritable.set(inputArray, 0, 5)
 
-    val converter = SparkContext.bytesWritableConverter()
+    val converter = WritableConverter.bytesWritableConverter()
     val byteArray = converter.convert(bytesWritable)
     assert(byteArray.length === 5)