# Functions inside of struct block
**URL:** https://discourse.julialang.org/t/functions-inside-of-struct-block/13462
**Category:** General Usage
**Created:** [August 14, 2018, 8:11pm UTC](https://discourse.julialang.org/t/functions-inside-of-struct-block/13462 "2018-08-14T20:11:11Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@galenlynch](https://discourse.julialang.org/u/galenlynch)
#### Post date: [August 14, 2018, 8:11pm UTC](https://discourse.julialang.org/t/functions-inside-of-struct-block/13462/1 "2018-08-14T20:11:11Z")
I noticed this code in `Pkg`, and the the utility of the `copy` function inside the struct block eludes me even though it’s commented:
```julia
struct VersionSet
intervals::Vector{VersionInterval}
VersionSet(intervals::Vector{VersionInterval}) = new(normalize!(intervals))
# copy is defined inside the struct block to call `new` directly
# without going through `normalize!`
Base.copy(vset::VersionSet) = new(copy(vset.intervals))
end
```
How is `copy` ever used? More generally, what is the scope of functions defined in the struct block?
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [August 14, 2018, 8:26pm UTC](https://discourse.julialang.org/t/functions-inside-of-struct-block/13462/2 "2018-08-14T20:26:50Z")
It doesn’t define a new function so there isn’t really any scope to talk about (except the one of the original function).
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### Author:  [@yurivish](https://discourse.julialang.org/u/yurivish)
#### Post date: [August 14, 2018, 8:30pm UTC](https://discourse.julialang.org/t/functions-inside-of-struct-block/13462/3 "2018-08-14T20:30:15Z")
To clarify Kristoffer’s comment, that line of code extends the same `Base.copy` as if it were defined outside the `struct`. The reason it is defined _inside_ is that it calls `new`, which is only accessible inside the scope of the `struct` definition.
The “function” `new` is ever only accessible from inside a `struct` definition, and directly constructs an instance of `VersionSet`, avoiding the constructor (which is defined here on the third line). That constructor does some work to preserve an invariant across all instances of `VersionSet`, but since the purpose of `copy` is to duplicate an existing pre-constructed `VersionSet`, we know that work can be avoided.
With a struct like this, where the inner constructor always does some work, the only way forward is to call `new` directly, which you can only do from inside the scope of a `struct` definition, which is why the extension of `Base.copy` ended up being put there – to have access to `new`.
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### Author:  [@galenlynch](https://discourse.julialang.org/u/galenlynch)
#### Post date: [August 14, 2018, 9:14pm UTC](https://discourse.julialang.org/t/functions-inside-of-struct-block/13462/4 "2018-08-14T21:14:28Z")
Ah I see now, thanks for the great explanation!