Assigning values to defined Tuple-array

New to Julia
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1

I am trying to create a tuple-array without assigning values to the tuples. Declaring tuples as an array runs smoothly:

tuples = Array{Tuple{Int, Int},2}
tuples[1] = (1,2)

However, trying to index any elements gives a “no matching setindex”-error. What happens when i declare tuples as an array, and why is it different than directly assigning values upon initialization?

Example, this runs fine:

tuples = [(1,2),(3,2)]
tuples[2]
2

Not sure I understand the question - are you saying what isn’t working is assigning to an index of an element of your array of tuples like

tup_arr = [(1,2), (3,4)]
tup_arr[1][1] = 5

?

This indeed throws a MethodError: no method matching setindex!, but this is unrelated to having an array of arrays and simply due to the fact that tuples are immutable:

t = (1,2)
t[1] = 5 # MethodError
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3

This is a type, not an object.

4

To be more concrete, I think what you meant to write may have been something like

julia> tuples = Array{Tuple{Int, Int},2}(undef, 1, 1)
1×1 Array{Tuple{Int64,Int64},2}:
 (4627041296, 4630374544)

julia> tuples[1] = (1,2)
(1, 2)
5

Okay, so by following the typedef with (undef, n, m) it will create an empty nxm Tuple-array?

6

It will create a n*m Tuple Array with ‘undefined’ contents. I.e. each element will just be a chunk of memory that has been interpreted as a Tuple{Int, Int}, so the contents will look like random garbage.

7

The beautiful thing about Julia is that you are not forced to fiddle with types if you don’t want to. In your case, for example, you can create a 2-by-3 array of tuples easily like this:

julia> tuples = similar([(0,0)], 2,3)
2×3 Array{Tuple{Int64,Int64},2}:
 (112936112, 94765632)   (94765632, 112941360)   (112514192, 112942032)
 (112514192, 112937040)  (112941488, 112115216)  (94765632, 4294967298)
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