Hello
I think you need to go back to the basics
Have you looked at the data sheet for this device?
You say you want to detect "metal" then talk about "magnets"
This device gives an output relative to a magnetic field, so a lump of aluminium isn't going to do much.
What do you mean by "slot"?
The Allegro site suggests that this is an end of life device, so maybe not the best choice.
I think your best bet is to decide what you really want to achieve - metal or magnet, choose a different device like the recommended A1308 replacement.
Allegro are generally pretty good at application notes, so I would start there, before even starting with code.
Just a quick look at the spec suggests that the output is analogue, so digital read may not be much good - I would expect this device to give a voltage output on the output pin, so analogue read would be more appropriate. Hall effect "switching" devices provide a digital output depending on the strength of the magnetic field.
Note that some of these devices need a load (resistor) on the output pin plus decoupling Vcc to GND
They are pretty resistant to abuse (getting it wired up incorrectly), but will only take so much.
Read the data sheet.