# Generator questions
**URL:** https://discourse.julialang.org/t/generator-questions/73665
**Category:** General Usage
**Tags:** generator
**Created:** [December 27, 2021, 12:25am UTC](https://discourse.julialang.org/t/generator-questions/73665 "2021-12-27T00:25:04Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [December 27, 2021, 12:25am UTC](https://discourse.julialang.org/t/generator-questions/73665/1 "2021-12-27T00:25:04Z")
While poking around with the generator example below to try understanding the concept, some questions popped up:
- Why is the last equality false given that the generator was regenerated?
- With the command `g.f(g.iter[n])`, are we materializing the nᵗʰ element of the generator?
```julia
A = [1 2; 3 4]
B = [A^i for i in 0:2]
g = (A*b for b in B) # creates generator
G = collect(g) # 3-element Vector{Matrix{Int64}}
g.f(g.iter[2]) == G[2] # true
g.f(g.iter[3]) == G[3] # true
g.iter[3] = ones(2,2) # assigned to a different matrix here
g.f(g.iter[3]) == G[3] # false (OK)
g = (A*b for b in B) # re-creates generator
g.f(g.iter[2]) == G[2] # true
g.f(g.iter[3]) == G[3] # false (why does the previous assignment still stand?)
```
Thank you.
---
### Author:  [@thautwarm](https://discourse.julialang.org/u/thautwarm)
#### Post date: [December 27, 2021, 2:15am UTC](https://discourse.julialang.org/t/generator-questions/73665/2 "2021-12-27T02:15:38Z")
> Why is the last equality false given that the generator was regenerated?
As there is no copy for `B`. The generator `g` holds the original reference of the iterator here:
```julia
julia> objectid(g.iter)
0x35595f9c567dff49
julia> objectid(B)
0x35595f9c567dff49
```
> With the command `g.f(g.iter[n])` , are we materializing the nᵗʰ element of the generator?
Only for `(... for element in array)` it can be `true`, but **in general it is not the case**.
There are two counterexamples to your guess.
1. not all generators use the notion of “nᵗʰ element”:
```julia
julia> res = ( [i, j] for i = 1: 2, j = 1:2)
julia> n = 1; res.iter[1]
ERROR: MethodError: no method matching getindex(::Base.Iterators.ProductIterator{Tuple{UnitRange{Int64}, UnitRange{Int64}}}, ::Int64)
```
1. we use the [iterator interface](https://docs.julialang.org/en/v1/manual/interfaces/#man-interface-iteration) to handle iterations. Random accessing is not available for iterables.
```julia
julia> using DataStructures
julia> xs = list(1, 2, 3)
list(1, 2, 3)
julia> g = (k * 2 for k in xs)
Base.Generator{Cons{Int64}, var"#17#18"}(var"#17#18"(), list(1, 2, 3))
julia> collect(g)
3-element Vector{Int64}:
2
4
6
g.iter[1]
ERROR: MethodError: no method matching getindex(::Cons{Int64}, ::Int64)
```