[GitHub] [flink] dawidwys commented on a change in pull request #8874: [FLINK-12968][table-common] Add a utility for logical type casts

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dawidwys commented on a change in pull request #8874: [FLINK-12968][table-common] Add a utility for logical type casts
URL: https://github.com/apache/flink/pull/8874#discussion_r297521021
 
 

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 File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/logical/utils/LogicalTypeCasts.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.types.logical.utils;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.table.types.logical.DateType;
+import org.apache.flink.table.types.logical.DistinctType;
+import org.apache.flink.table.types.logical.LogicalType;
+import org.apache.flink.table.types.logical.LogicalTypeFamily;
+import org.apache.flink.table.types.logical.LogicalTypeRoot;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.BINARY_STRING;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.CHARACTER_STRING;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.CONSTRUCTED;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.DATETIME;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.EXACT_NUMERIC;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.INTERVAL;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.NUMERIC;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.PREDEFINED;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.TIME;
+import static org.apache.flink.table.types.logical.LogicalTypeFamily.TIMESTAMP;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.ANY;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.BIGINT;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.BINARY;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.BOOLEAN;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.CHAR;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.DATE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.DECIMAL;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.DISTINCT_TYPE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.DOUBLE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.FLOAT;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.INTEGER;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.INTERVAL_DAY_TIME;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.INTERVAL_YEAR_MONTH;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.NULL;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.SMALLINT;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.STRUCTURED_TYPE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.SYMBOL;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.TIMESTAMP_WITHOUT_TIME_ZONE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.TIMESTAMP_WITH_LOCAL_TIME_ZONE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.TIMESTAMP_WITH_TIME_ZONE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.TIME_WITHOUT_TIME_ZONE;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.TINYINT;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.VARBINARY;
+import static org.apache.flink.table.types.logical.LogicalTypeRoot.VARCHAR;
+import static org.apache.flink.table.types.logical.utils.LogicalTypeChecks.hasFamily;
+import static org.apache.flink.table.types.logical.utils.LogicalTypeChecks.isSingleFieldInterval;
+
+/**
+ * Utilities for casting {@link LogicalType}.
+ *
+ * <p>This class aims to be compatible with the SQL standard cast specification.
+ *
+ * <p>Conversions that are defined by the {@link LogicalType} (e.g. interpreting a {@link DateType}
+ * as integer value) are not considered here. They are an internal bridging feature that is not
+ * standard compliant. If at all, {@code CONVERT} methods should make such conversions available.
+ */
+@Internal
+public final class LogicalTypeCasts {
+
+	private static final Map<LogicalTypeRoot, Set<LogicalTypeRoot>> implicitCastingRules;
+
+	private static final Map<LogicalTypeRoot, Set<LogicalTypeRoot>> explicitCastingRules;
+
+	static {
+		implicitCastingRules = new HashMap<>();
+		explicitCastingRules = new HashMap<>();
+
+		// identity casts
+
+		for (LogicalTypeRoot typeRoot : allTypes()) {
+			castTo(typeRoot)
+				.implicitFrom(typeRoot)
+				.build();
+		}
+
+		// cast specification
+
+		castTo(CHAR)
+			.implicitFrom(CHAR)
+			.explicitFromFamily(PREDEFINED)
+			.explicitNotFromFamily(BINARY_STRING)
+			.build();
+
+		castTo(VARCHAR)
+			.implicitFromFamily(CHARACTER_STRING)
+			.explicitFromFamily(PREDEFINED)
+			.explicitNotFromFamily(BINARY_STRING)
+			.build();
+
+		castTo(BOOLEAN)
+			.implicitFrom(BOOLEAN)
+			.explicitFromFamily(CHARACTER_STRING)
+			.build();
+
+		castTo(BINARY)
+			.implicitFromFamily(BINARY_STRING)
+			.build();
+
+		castTo(VARBINARY)
+			.implicitFromFamily(BINARY_STRING)
+			.build();
+
+		castTo(DECIMAL)
+			.implicitFromFamily(NUMERIC)
+			.explicitFromFamily(CHARACTER_STRING)
+			.build();
+
+		castTo(TINYINT)
+			.implicitFrom(TINYINT)
+			.explicitFromFamily(NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(SMALLINT)
+			.implicitFrom(TINYINT, SMALLINT)
+			.explicitFromFamily(NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(INTEGER)
+			.implicitFrom(TINYINT, SMALLINT, INTEGER)
+			.explicitFromFamily(NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(BIGINT)
+			.implicitFrom(TINYINT, SMALLINT, INTEGER, BIGINT)
+			.explicitFromFamily(NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(FLOAT)
+			.implicitFrom(TINYINT, SMALLINT, INTEGER, BIGINT, FLOAT, DECIMAL)
+			.explicitFromFamily(NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(DOUBLE)
+			.implicitFrom(TINYINT, SMALLINT, INTEGER, BIGINT, FLOAT, DOUBLE, DECIMAL)
+			.explicitFromFamily(CHARACTER_STRING)
+			.build();
+
+		castTo(DATE)
+			.implicitFrom(DATE, TIMESTAMP_WITHOUT_TIME_ZONE)
+			.explicitFromFamily(TIMESTAMP, CHARACTER_STRING)
+			.build();
+
+		castTo(TIME_WITHOUT_TIME_ZONE)
+			.implicitFrom(TIME_WITHOUT_TIME_ZONE, TIMESTAMP_WITHOUT_TIME_ZONE)
+			.explicitFromFamily(TIME, TIMESTAMP, CHARACTER_STRING)
+			.build();
+
+		castTo(TIMESTAMP_WITHOUT_TIME_ZONE)
+			.implicitFrom(TIMESTAMP_WITHOUT_TIME_ZONE)
+			.explicitFromFamily(DATETIME, CHARACTER_STRING)
+			.build();
+
+		castTo(TIMESTAMP_WITH_TIME_ZONE)
+			.implicitFrom(TIMESTAMP_WITH_TIME_ZONE)
+			.explicitFromFamily(DATETIME, CHARACTER_STRING)
+			.build();
+
+		castTo(TIMESTAMP_WITH_LOCAL_TIME_ZONE)
+			.implicitFrom(TIMESTAMP_WITH_LOCAL_TIME_ZONE)
+			.explicitFromFamily(DATETIME, CHARACTER_STRING)
+			.build();
+
+		castTo(INTERVAL_YEAR_MONTH)
+			.implicitFrom(INTERVAL_YEAR_MONTH)
+			.explicitFromFamily(EXACT_NUMERIC, CHARACTER_STRING)
+			.build();
+
+		castTo(INTERVAL_DAY_TIME)
+			.implicitFrom(INTERVAL_DAY_TIME)
+			.explicitFromFamily(EXACT_NUMERIC, CHARACTER_STRING)
+			.build();
+	}
+
+	public static boolean supportsImplicitCast(LogicalType sourceType, LogicalType targetType) {
 
 Review comment:
   Could you add a javadoc here with an example what is implicit cast. The same for explicit?

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