org.partiql.lang.ast.IsPathIndexMeta.kt Maven / Gradle / Ivy

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An implementation of PartiQL for the JVM written in Kotlin.

There is a newer version: 1.0.0-perf.1

/*
 * Copyright 2019 Amazon.com, Inc. or its affiliates.  All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 *  You may not use this file except in compliance with the License.
 * A copy of the License is located at:
 *
 *      http://aws.amazon.com/apache2.0/
 *
 *  or in the "license" file accompanying this file. This file 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.partiql.lang.ast

/**
 * This is used by the PartiQLVisitor to determine whether the path step is of type index. This is because it is
 * used to evaluate path expressions in FROM clauses in convertPathToProjectionItem(). This class exists because ANTLR
 * first parses the path (and adds [IsPathIndexMeta] to any path step that uses indexing: AKA a[0]), and, upon visiting
 * the path, we check that the path doesn't end with a `.*` and contains an index. The AST does
 * not differentiate between different path steps, and therefore, this meta exists to aid in determining whether the
 * projection item path is correct.
 * Example:
 *   - ```SELECT a.b.* FROM data``` --> Allowed
 *   - ```SELECT a[b] FROM data``` --> Allowed
 *   - ```SELECT a[b].* FROM data``` --> NOT Allowed
 */
class IsPathIndexMeta private constructor() : Meta {
    override val tag = TAG

    companion object {
        const val TAG = "\$is_path_index"

        val instance = IsPathIndexMeta()
    }
}