Late response but for those who live here, are moving here, or will be visiting you need to look at the state law as posted above (the RCW) AND the laws of each city you will be in. Unlike firearms there is no preemption here. Each city is free to pass whatever knife restrictions it wants to.
Seattle bans folders with a blade over 3.5", and all fixed blade knives unless worn openly for work, hiking, or fishing. Or stored in a toolbox.
Tacoma has a 3.5 inch limit on any knives.
Everett and Yelm both have 3 inch limits.
Other cities will have their own restrictions or none at all.
Assisted openers are completely legal.
Automatics, no matter how they open are banned for almost everyone. The only exceptions are on-duty police (only full time, paid cops though, reserve don't count. The term is "general authority law enforcement officer," and the definition includes full time and fully compensated.), on duty military/NG, on duty EMTs, and on duty firefighters. Transport to and from where they are stored while not on duty is also ok.
There was this myth that you could have but not carry an automatic. Maybe the interpretation of the 1959 wording that says, "have in his possession."