[
https://issues.apache.org/jira/browse/GROOVY-10943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17695186#comment-17695186
]
ASF GitHub Bot commented on GROOVY-10943:
-----------------------------------------
Goooler commented on code in PR #1867:
URL: https://github.com/apache/groovy/pull/1867#discussion_r1122002346
##########
src/main/java/org/apache/groovy/parser/antlr4/AstBuilder.java:
##########
@@ -3906,13 +3906,17 @@ private void validateParameterList(final
List<Parameter> parameterList) {
for (int n = parameterList.size(), i = n - 1; i >= 0; i -= 1) {
Parameter parameter = parameterList.get(i);
+ String name = parameter.getName();
+ if (name.equals("_")) {
Review Comment:
```suggestion
if ("_".equals(name)) {
```
##########
src/main/java/org/codehaus/groovy/control/PlaceholderVisitor.java:
##########
@@ -0,0 +1,68 @@
+/*
+ * 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.codehaus.groovy.control;
+
+import org.codehaus.groovy.ast.ASTNode;
+import org.codehaus.groovy.ast.ClassCodeVisitorSupport;
+import org.codehaus.groovy.ast.expr.ClosureExpression;
+import org.codehaus.groovy.ast.expr.DeclarationExpression;
+import org.codehaus.groovy.ast.expr.VariableExpression;
+
+import java.util.stream.StreamSupport;
+
+public class PlaceholderVisitor extends ClassCodeVisitorSupport {
+ public static final String PLACEHOLDER = "Underscore_Placeholder";
+ private SourceUnit source;
+
+ public PlaceholderVisitor(CompilationUnit compilationUnit, SourceUnit
source) {
+ this.source = source;
+ }
+
+ @Override
+ public void visitDeclarationExpression(DeclarationExpression expression) {
+ if (expression.isMultipleAssignmentDeclaration() &&
expression.getTupleExpression().getExpressions().size() > 1) {
+ long underscoreCount =
StreamSupport.stream(expression.getTupleExpression().spliterator(), false)
+ .map(e -> ((VariableExpression) e).getName())
+ .filter(s -> s.equals("_"))
+ .count();
+ if (underscoreCount > 1) {
+ expression.getTupleExpression().getExpressions().forEach(e -> {
+ if (((VariableExpression) e).getName().equals("_")) {
Review Comment:
```suggestion
String name = ((VariableExpression) e).getName();
if ("_".equals(name)) {
```
> Consider additional use of _ as a placeholder
> ---------------------------------------------
>
> Key: GROOVY-10943
> URL: https://issues.apache.org/jira/browse/GROOVY-10943
> Project: Groovy
> Issue Type: Improvement
> Reporter: Paul King
> Priority: Major
> Labels: GEP
>
> Recent Java versions make underscore, "_", an illegal variable name. This is
> to allow it to be used as a placeholder as per JEP 302: Lambda Leftovers[1].
> This issue is to explore how better to have such a placeholder in Groovy.
> This strengthens an informal convention already in use. Instead of writing
> this:
> {code}
> def (coordX, coordY, unusedZ) = coord3D()
> {code}
> Sometimes it is written as:
> {code}
> def (coordX, coordY, _) = coord3D()
> {code}
> Currently, the underscore is a variable and could be used but the convention
> is that
> it would be ignored.
> This convention doesn't scale if more than one result is to be ignored (here
> a double underscore is used for the second ignored result):
> {code}
> def (coordX, coordY, _, __) = coord3DwithColor()
> {code}
> This idea being that the following should be valid:
> {code}
> def (coordX, coordY, _, _) = coord3DwithColor()
> {code}
> Which currently gives an error for the duplicated variable name.
> Another example:
> {code}
> def (x, _, y, _, z) = 1..5
> assert "$x $y $z" == '1 3 5'
> {code}
> Similarly, the idea is applicable for lambda parameters (as per the example
> in the previously mentioned Java JEP):
> {code}
> BiFunction<Integer, String, String> biss = (i, _) -> String.valueOf(i)
> {code}
> We could follow Java's lead and make underscore an invalid variable name but
> it might be possible to keep uses of that name except where there is more
> than one occurrence of the name. In such a circumstance, use of the name
> would no longer reference a variable. We need to check the impacts of
> shadowing as per discussions in the JEP.
> [1] [https://openjdk.org/jeps/302]
>
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