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Read the for-loop enumerator out of its KeyValuePair once #2143

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Merged
slozier merged 1 commit into from
Nov 4, 2026
Merged

Read the for-loop enumerator out of its KeyValuePair once #2143

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30 changes: 19 additions & 11 deletions src/core/IronPython/Compiler/Ast/ForStatement.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -74,18 +74,26 @@ internal static MSAst.Expression TransformFor(ScopeStatement parent, MSAst.Param
)
);

// while enumerator.MoveNext():
// left = enumerator.Current
// iterator = enumerator.Key
// read once, because the interpreter calls a property getter of a struct through reflection
MSAst.ParameterExpression iterator = Ast.Variable(typeof(IEnumerator), "foreach_iterator");
MSAst.Expression initIterator = Ast.Assign(
iterator,
Ast.Property(
enumerator,
typeof(KeyValuePair<IEnumerator, IDisposable>).GetProperty("Key")
)
);

// while iterator.MoveNext():
// left = iterator.Current
// body
// else:
// else
MSAst.Expression ls = AstUtils.Loop(
parent.GlobalParent.AddDebugInfo(
Ast.Call(
Ast.Property(
enumerator,
typeof(KeyValuePair<IEnumerator, IDisposable>).GetProperty("Key")
),
iterator,
typeof(IEnumerator).GetMethod("MoveNext")
),
left.Span
Expand All @@ -95,10 +103,7 @@ internal static MSAst.Expression TransformFor(ScopeStatement parent, MSAst.Param
left.TransformSet(
SourceSpan.None,
Ast.Call(
Ast.Property(
enumerator,
typeof(KeyValuePair<IEnumerator, IDisposable>).GetProperty("Key")
),
iterator,
typeof(IEnumerator).GetProperty("Current").GetGetMethod()
),
PythonOperationKind.None
Expand All @@ -113,12 +118,15 @@ internal static MSAst.Expression TransformFor(ScopeStatement parent, MSAst.Param
);

return Ast.Block(
[iterator],
init,
initIterator,
Ast.TryFinally(
ls,
Ast.Block(
Ast.Call(AstMethods.ForLoopDispose, enumerator),
Ast.Assign(enumerator, Ast.New(typeof(KeyValuePair<IEnumerator, IDisposable>)))
Ast.Assign(enumerator, Ast.New(typeof(KeyValuePair<IEnumerator, IDisposable>))),
Ast.Assign(iterator, AstUtils.Constant(null, typeof(IEnumerator)))
)
)
);
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