@a = map { $_ = 3; } [];
[download]

is no more or less junk than

@a = map { $_ = 3; } $x.$y;
[download]

Are you therefore talking about [] + 1? Making the reference read-only is not going to catch that.

There are far more situations where it might make sense to append or add something to a simple type.

Not so with refs, no way a .= or a += will lead to anything meaningful.

Well except when blessed and overloaded. But that's far fetched.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

Making the var read-only won't prevent concatenation or addition, so it doesn't matter that $x . [] or $x + [] doesn't make sense.^[1]. This isn't relevant to the topic at hand.

The only thing making it read-only will do is prevent assignment, and map { $_ = 3 } $x.$y makes no more sense than map { $_ = 3 } [].

Either prevent both of them, or prevent neither of them. No need for baseless inconsistencies.

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1. That said, $ref+0 makes some sense for refs to things other than objects with overloads, and both concatenation and addition make sense for refs to objects with overloads (which aren't farfetched at all!)