We require "var" before variable patterns because we also allow named constants in patterns (which match if the value is equal to the constant's value):

    const pi = 3.14; // Close enough.

    switch (value) {
      (pi, var pi) => ...
    }

This case matches a record whose first field is equal to 3.14 and binds the second field to a new variable named "pi". Of course, in practice, you wouldn't actually shadow a constant like this, but we didn't want pattern syntax to require name resolution to be unambiguous, so in contexts where a constant pattern is allowed, we require you to write "var", "final", or a type to indicate when you want to declare a variable.

Swift's pattern syntax works pretty much the same way.

> > Dart doesn't have symbols

> That's weird, as I actually use sometimes `#sym` (which has type `Symbol`)??

Oh, right. I always forget about those. Yes, technically we have symbols, but they are virtually unused and are a mostly pointless wart on the language. It's not idiomatic to use them like it is in Ruby.