### Author:  [@Ibb](https://discourse.julialang.org/u/Ibb)
#### Post date: [September 28, 2020, 10:33am UTC](https://discourse.julialang.org/t/correct-way-to-dereference-large-memory/47395/3 "2020-09-28T10:33:04Z")
Thx for advise, but it seems that NTuple{36000, UInt8} doesn’t store Undef data. What I want to do is to read a binary file right into a large struct or tuple. Code below won’t work either.
```julia
julia> struct LargeStruct
value::NTuple{36000, UInt8}
end
julia> sizeof(LargeStruct) #36000
julia> large_struct = Ref{LargeStruct}()
julia> read!(, large_struct)
julia> large_struct[].value[1]
```
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### Author:  [@jakobnissen](https://discourse.julialang.org/u/jakobnissen)
#### Post date: [September 28, 2020, 10:44am UTC](https://discourse.julialang.org/t/correct-way-to-dereference-large-memory/47395/4 "2020-09-28T10:44:07Z")
The problem here is not actually the referencing or the memory. Your code is fine. It’s the fact that Julia’s compiler handles large immutable struct like tuples very badly. So badly in fact that large structs are unusable in Julia.
Hopefully this will be adressed in the future - it’s certainly something I’ve seen mentioned many times, and is an annoying limitation to Julia.
For now, the solution is to limit the size of immutable structs to, say, 100 fields, and use heap-allocated vectors instead, i.e. `Vector{UInt8}`.
---
### Author:  [@Ibb](https://discourse.julialang.org/u/Ibb)
#### Post date: [September 28, 2020, 10:57am UTC](https://discourse.julialang.org/t/correct-way-to-dereference-large-memory/47395/5 "2020-09-28T10:57:20Z")
Thx a lot for your answer. I think I need to parse my binary files “field by field” now.
---
### Author:  [@stephancb](https://discourse.julialang.org/u/stephancb)
#### Post date: [September 28, 2020, 11:30am UTC](https://discourse.julialang.org/t/correct-way-to-dereference-large-memory/47395/6 "2020-09-28T11:30:25Z")
You might have a look at [Memory-mapped I/O · The Julia Language](https://docs.julialang.org/en/v1/stdlib/Mmap/)
---
### Author:  [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)
#### Post date: [September 28, 2020, 1:34pm UTC](https://discourse.julialang.org/t/correct-way-to-dereference-large-memory/47395/7 "2020-09-28T13:34:02Z")
uhhh, I may have missed something, but seems to me that the real problem here is that Tuple are immutable objects, so it does not make sense to create a uninitialized tuple object to then try to read data into it.
What others said is true, you should avoid using large Tuples, they are not performant. I think the threshold where performance takes a hit is 32+ elements, but I may be wrong.