I'm glad I'm not the only one thinking this. What's the point of Swift being "safer" if this isn't an error (or at least a warning). The standard library even includes -[mutableCopy], so it's a established convention.
agreed; this would be a nice exception and I'm sure in a few places the compiler could pick this up to add warnings.
Alternatively get it to throw an exception if the array is modified.
Much better than some [[]] notation which just makes me think of multidimensional arrays
