I actually prefer a ternary arrangement that lets you chain arbitrary such expressions like a truth table:

    return (value >= radix) ? error.InvalidChar:
           (comeCondition)  ? error.OtherError:
           ...
                              value;

I like doing that too, but the Zig syntax doesn't prevent that kind of arrangement, just makes it a bit wider.

    return if (value >= radix) error.InvalidChar else
           if (comeCondition)  error.OtherError  else
           ...
                               value;

or maybe this, but it seems uglier to me:

    return if      (value >= radix) error.InvalidChar
           else if (comeCondition)  error.OtherError
           ...
           else                     value;