Is it possible to look up values in an array or a dict using integer variables?

Something like

```
@variable(model, x, Int)
# restrict x to appropriate values
@constraint(model, my_array[x] <= 5)
```

Or should a binary array with a single one be created and summed over to implement the look up? Like:

```
@variable(model, x[1:n], Bin)
@constraint(model, sum(x[i] for i in 1:n) ==1)
@constraint(model, sum(x[i]*my_array[i] for i in 1:n) <= 5)
```

Is this where you use something like MOI.SOS1? Can you use SOS1 on an array of arrays?