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https://issues.apache.org/jira/browse/GROOVY-11629?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17947539#comment-17947539
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Oscar N commented on GROOVY-11629:
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I think you could support parameters, variables and field references when
they're either marked as final or are never re-assigned (effectively-final).
> Redundant null check on @NullChecked parameter when iterating on it
> -------------------------------------------------------------------
>
> Key: GROOVY-11629
> URL: https://issues.apache.org/jira/browse/GROOVY-11629
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 5.0.0-alpha-12, 3.0.24, 4.0.26
> Reporter: Oscar N
> Priority: Minor
>
> When looping over a method parameter whose method is annotated with
> @NullCheck, an additional null check performed before iterating. Here's a
> minimal example, demonstrating the numbers parameter being checked for null
> twice:
> {code:groovy}
> import groovy.transform.CompileStatic
> import groovy.transform.NullCheck
> void main() {
> listNumbers([1, 2, 3])
> }
> @CompileStatic
> @NullCheck
> void listNumbers(List<Number> numbers) {
> for (number in numbers)
> println number
> }
> {code}
> Decompiled Java representation of the bytecode:
> {code:java}
> public void listNumbers(List<Number> numbers) {
> if (numbers == null) {
> throw (Throwable)(new IllegalArgumentException("numbers cannot be
> null"));
> } else {
> Iterator var10000 = numbers != null ? numbers.iterator() : null;
> Object number = null;
> Iterator var4 = var10000;
> if (var4 != null) {
> while(var4.hasNext()) {
> number = var4.next();
> DefaultGroovyMethods.println(this, number);
> Object var6 = null;
> }
> }
> }
> }
> {code}
> Bytecode:
> {code:java}
> // access flags 0x1
> // signature (Ljava/util/List<Ljava/lang/Number;>;)V
> // declaration: void listNumbers(java.util.List<java.lang.Number>)
> public listNumbers(Ljava/util/List;)V
> L0
> ALOAD 1
> IFNONNULL L1
> ICONST_1
> GOTO L2
> L1
> ICONST_0
> L2
> IFEQ L3
> NEW java/lang/IllegalArgumentException
> DUP
> LDC "numbers cannot be null"
> INVOKESPECIAL java/lang/IllegalArgumentException.<init>
> (Ljava/lang/String;)V
> CHECKCAST java/lang/Throwable
> ATHROW
> L3
> LINENUMBER 11 L3
> ALOAD 1
> DUP
> ASTORE 2
> IFNULL L4
> ALOAD 2
> INVOKEINTERFACE java/util/List.iterator ()Ljava/util/Iterator; (itf)
> GOTO L5
> L4
> ACONST_NULL
> L5
> ACONST_NULL
> ASTORE 3
> L6
> ASTORE 4
> ALOAD 4
> IFNULL L7
> L8
> ALOAD 4
> INVOKEINTERFACE java/util/Iterator.hasNext ()Z (itf)
> IFEQ L7
> ALOAD 4
> INVOKEINTERFACE java/util/Iterator.next ()Ljava/lang/Object; (itf)
> ASTORE 3
> L9
> LINENUMBER 12 L9
> ALOAD 0
> ALOAD 3
> INVOKESTATIC org/codehaus/groovy/runtime/DefaultGroovyMethods.println
> (Ljava/lang/Object;Ljava/lang/Object;)V
> ACONST_NULL
> POP
> GOTO L8
> L7
> LINENUMBER 13 L7
> RETURN
> LOCALVARIABLE this LRedundantNullCheck; L0 L7 0
> LOCALVARIABLE numbers Ljava/util/List; L0 L7 1
> LOCALVARIABLE number Ljava/lang/Object; L6 L7 3
> MAXSTACK = 3
> MAXLOCALS = 5
> {code}
> Note that this also happens in CompileDynamic mode.
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