[calcite] 02/05: [CALCITE-4226] Add Mappings#asListNonNull as a null-safe alternative for Mappings#asList

[vladimirsitnikov]

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vladimirsitnikov pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/calcite.git

commit 9422fd444f0cb01cf5659045d1bb3bc71b59b73e
Author: Vladimir Sitnikov <sitnikov.vladi...@gmail.com>
AuthorDate: Fri Sep 4 23:29:30 2020 +0300

    [CALCITE-4226] Add Mappings#asListNonNull as a null-safe alternative for 
Mappings#asList
---
 .../org/apache/calcite/util/mapping/Mappings.java  | 27 ++++++++++++++++++++++
 .../apache/calcite/util/mapping/MappingTest.java   | 13 ++++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java 
b/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
index 9162d40..88d2c7e 100644
--- a/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
+++ b/core/src/main/java/org/apache/calcite/util/mapping/Mappings.java
@@ -326,6 +326,33 @@ public abstract class Mappings {
   }
 
   /**
+   * Returns a mapping as a list such that {@code list.get(source)} is
+   * {@code mapping.getTarget(source)} and {@code list.size()} is
+   * {@code mapping.getSourceCount()}.
+   *
+   * <p>The resulting list never contains null elements</p>
+   *
+   * <p>Converse of {@link #target(List, int)}</p>
+   * @see #asList(TargetMapping)
+   */
+  public static List<Integer> asListNonNull(final TargetMapping mapping) {
+    return new AbstractList<Integer>() {
+      public Integer get(int source) {
+        int target = mapping.getTargetOpt(source);
+        if (target < 0) {
+          throw new IllegalArgumentException("Element " + source + " is not 
found in mapping "
+              + mapping);
+        }
+        return target;
+      }
+
+      public int size() {
+        return mapping.getSourceCount();
+      }
+    };
+  }
+
+  /**
    * Converts a {@link Map} of integers to a {@link TargetMapping}.
    */
   public static TargetMapping target(
diff --git 
a/core/src/test/java/org/apache/calcite/util/mapping/MappingTest.java 
b/core/src/test/java/org/apache/calcite/util/mapping/MappingTest.java
index 9be5938..42a41a7 100644
--- a/core/src/test/java/org/apache/calcite/util/mapping/MappingTest.java
+++ b/core/src/test/java/org/apache/calcite/util/mapping/MappingTest.java
@@ -171,7 +171,10 @@ class MappingTest {
     assertThrows(IndexOutOfBoundsException.class, () -> mapping.getTarget(-1));
 
     final List<Integer> integers = Mappings.asList(mapping);
-    assertThat(integers, equalTo(targets));
+    assertThat("Mappings.asList" + mapping + ")", integers, equalTo(targets));
+    assertThat(
+        "Mappings.asListNonNull(" + mapping + ")",
+        Mappings.asListNonNull(mapping), equalTo(targets));
 
     final Mapping inverse = mapping.inverse();
     assertThat(inverse.toString(),
@@ -200,6 +203,14 @@ class MappingTest {
     final List<Integer> integers = Mappings.asList(mapping);
     assertThat(integers,
         equalTo(Arrays.asList(null, 1, null, 0, 2, 3, null, null, 4, null)));
+
+    // Note: exception is thrown on list.get, so it is needed to trigger the 
exception
+    IllegalArgumentException exception =
+        assertThrows(IllegalArgumentException.class, () ->
+            Mappings.asListNonNull(mapping).get(0));
+    assertThat(exception.getMessage(),
+        equalTo("Element 0 is not found in mapping [size=5, sourceCount=10, 
targetCount=5"
+            + ", elements=[1:1, 3:0, 4:2, 5:3, 8:4]]"));
   }
 
   /** Unit test for {@link Mappings#bijection(List)}. */