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[spec/statement] Clarify foreach restrictions #22917

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[spec/statement] Clarify foreach restrictions #22917

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3 changes: 3 additions & 0 deletions spec/statement.dd
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Expand Up @@ -1274,6 +1274,9 @@ $(H3 $(LNAME2 foreach_restrictions, Foreach Restrictions))
while `foreach` is iterating over the elements.
)

$(UNDEFINED_BEHAVIOR If one of those operations occurs and it is `@system`.)
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@dkorpel dkorpel Apr 13, 2026

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Does 'it' refer to the operation or the enclosing function? The latter makes more sense to me, but the wording implies the former.

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@ntrel ntrel Apr 15, 2026

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@dkorpel I think if the operation is allowed in @safe code, it should be implementation-defined iff it happens in @system code which doesn't do anything unsafe (or it does something unsafe that is unrelated to the operation).

$(IMPLEMENTATION_DEFINED If resizing or reassignment occurs and it is `@safe`.)

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int[] a = [1, 2, 3];
auto fun = { a ~= 4; };
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