Whats the difference between newSlot and setSlot in the Io Language?

Question

In the Io Language, there are 2 methods for creating slots: newSlot and setSlot. Both seem to have similar behavior except newSlot also creates a setter. What cases are there for a needing a setter to be created at the same time as slot creation? What exactly is the purpose of the setter anyway?

I was also wondering what a setter was at the end of the first day of Io in 7 languages in 7 weeks. — Jedidja, Oct 18 '12 at 20:20

score 35 · Accepted Answer · edited Apr 21 '17 at 15:39

I believe its a convenience which provides good coding practises. Thus if you want to expose an objects attribute then newSlot or its synonym ::= are the preferred way to go.

newSlot can make things look nicer. For eg.

Animal := Object clone do (
    legs ::= nil    // creates leg slot  & setLegs() setter
    tail ::= nil    // creates tail slot & setTail() setter
)

// I think below is more aesthetic 
Cat := Animal clone setLegs(4) setTail(1)

// compared to this
Dog := Animal clone do (legs = 4; tail = 1)

And also it can get around do() context. For eg.

Pet := Animal clone do (
    name ::= nil
)

myPetCats := list("Ambrose", "Fluffy", "Whiskers") map (petName,
    Pet clone do (name = petName)   // throws exception
)

The Pet clone do (name = petName) will die throwing Exception: Pet does not respond to 'petName' because do() is interpreted within the cloned Pet context and so it cannot see petName.

So instead you need to use the setter:

myPetCats := list("Ambrose", "Fluffy", "Whiskers") map (petName,
    Pet clone setName(petName)
)

Whats the difference between newSlot and setSlot in the Io Language?

1 Answers1