Reuse short Char and Varchar type instances

Share ("cache") instances for short `char` and `varchar` types.
- type instantiation can be expensive (see
  96a009e)
- it allows caching things further, like in `getRange()`.

core/trino-spi/src/main/java/io/trino/spi/type/CharType.java

@@ -49,6 +49,13 @@ public final class CharType
     private static final TypeOperatorDeclaration TYPE_OPERATOR_DECLARATION = extractOperatorDeclaration(CharType.class, lookup(), Slice.class);
 
     public static final int MAX_LENGTH = 65_536;
+    private static final CharType[] CACHED_INSTANCES = new CharType[128];
+
+    static {
+        for (int i = 0; i < CACHED_INSTANCES.length; i++) {
+            CACHED_INSTANCES[i] = new CharType(i);
+        }
+    }
 
     private final int length;
     private volatile Optional<Range> range;
@@ -67,6 +74,9 @@ public static CharType createCharType(long length)
 
     public static CharType createCharType(int length)
     {
+        if (0 <= length && length < CACHED_INSTANCES.length) {
+            return CACHED_INSTANCES[length];
+        }
         return new CharType(length);
     }
 

core/trino-spi/src/main/java/io/trino/spi/type/VarcharType.java

@@ -48,6 +48,14 @@ public final class VarcharType
     public static final int MAX_LENGTH = Integer.MAX_VALUE - 1;
     public static final VarcharType VARCHAR = new VarcharType(UNBOUNDED_LENGTH);
 
+    private static final VarcharType[] CACHED_INSTANCES = new VarcharType[128];
+
+    static {
+        for (int i = 0; i < CACHED_INSTANCES.length; i++) {
+            CACHED_INSTANCES[i] = new VarcharType(i);
+        }
+    }
+
     public static VarcharType createUnboundedVarcharType()
     {
         return VARCHAR;
@@ -59,6 +67,9 @@ public static VarcharType createVarcharType(int length)
             // Use createUnboundedVarcharType for unbounded VARCHAR.
             throw new IllegalArgumentException("Invalid VARCHAR length " + length);
         }
+        if (length < CACHED_INSTANCES.length) {
+            return CACHED_INSTANCES[length];
+        }
         return new VarcharType(length);
     }