# O.O.P in Julia

**URL:** <https://discourse.julialang.org/t/o-o-p-in-julia/124957>\
**Category:** General Usage\
**Created:** [January 20, 2025, 11:09am UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957 "2025-01-20T11:09:00Z")\
**Posts on this page:** 6\
**Page:** 2

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**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [January 21, 2025, 3:10pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/21 "2025-01-21T15:10:17Z")

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No need to make it work with `object.value` syntax. It’s not very Julian anyway. Personally, I hide almost all `object.value` calls behind a getter as it makes refactors easier later. Use a global and have a accessor function that gets/sets it. Here’s an example:

```julia
const Type1_goodness = Ref(3.0) # use Ref to make it mutable

struct Type1
    bigness::Float64
end

struct Type2
    bigness::Float64
    coolness::Float64
    goodness::Float64
end

bigness(x::Type1) = x.bigness
coolness(x::Type1) = 2.0 # hard-coded, but could also reference a global const if it makes sense
goodness(x::Type1) = Type1_goodness[] # access the global const Ref
setgoodness!(x::Type1, val) = Type1_goodness[] = val # set the global

bigness(x::Type2) = x.bigness
coolness(x::Type2) = x.coolness
goodness(x::Type2) = x.goodness
# cannot setgoodness!(::Type2, val) because it is not mutable
# but you could make it construct a new Type2 with the new goodness and *not* mutate the original, depending on your needs

coolness(Type1(4.0)) # 2.0 - not a field but we can still get the value
coolness(Type2(5.0, 6.0, 7.0)) # 6.0 - read the field

goodness(Type1(4.0)) # 3.0 - the original default value
setgoodness!(Type1(4.0), 9.0) # 9.0 - we've set the value for all Type1 now
goodness(Type1(8.0)) # 9.0 - read the shared value

```

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<div class="post-metadata">

**Author:** ![world-peace](https://avatars.discourse-cdn.com/v4/letter/w/9f8e36/32.png) [@world-peace](https://discourse.julialang.org/u/world-peace)\
**Post date:** [January 21, 2025, 3:36pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/22 "2025-01-21T15:36:37Z")

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**Author:** ![Nathan\_Boyer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nathan_boyer/32/14825_2.png) [@Nathan\_Boyer](https://discourse.julialang.org/u/Nathan_Boyer)\
**Post date:** [January 21, 2025, 4:00pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/23 "2025-01-21T16:00:01Z")

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<div class="post-metadata">

**Author:** ![Marco\_Antoniotti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marco_antoniotti/32/18697_2.png) [@Marco\_Antoniotti](https://discourse.julialang.org/u/Marco_Antoniotti)\
**Post date:** [January 24, 2025, 3:55pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/24 "2025-01-24T15:55:05Z")

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Yep…

Question is: why not do what granddaddy (the guy with parentheses) does (right)?

That is, creating the “getter” automatically? 🙂

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<div class="post-metadata">

**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [January 24, 2025, 4:11pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/25 "2025-01-24T16:11:37Z")

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Consider `getproperty` the automatic getter. But it’s limited (yes, you can redefine `getproperty` but that isn’t very ergonomic). You also can’t (with `.property` syntax) provide additional arguments to `getproperty`, which you might later decide you want for certain properties.

Suppose I removed the `goodness` field from `Type2` because I decided I wanted it to be defined by `goodness(x::Type2) = bigness(x) + coolness(x)`. Multiple dispatch and extensibility are easy for getters but a total pain for `getproperty`. That’s where this pattern starts to be more useful. The larger the number of “inter-compatible” types you start to get, the more useful it is to be able to easily and orthogonally define behavior with methods rather than amending an increasingly complicated `getproperty`.

Obviously both approaches can work, but in my travels I’ve sometimes regretted relying on `getproperty` but never getters.

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<div class="post-metadata">

**Author:** ![Marco\_Antoniotti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marco_antoniotti/32/18697_2.png) [@Marco\_Antoniotti](https://discourse.julialang.org/u/Marco_Antoniotti)\
**Post date:** [January 24, 2025, 4:26pm UTC](https://discourse.julialang.org/t/o-o-p-in-julia/124957/26 "2025-01-24T16:26:53Z")

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Weeeellll

```Lisp
(defstruct type-1 bigness)
(defstruct (type-2 (:include type-2)) coolness goodness)

```

Do TRT (granddaddy knows a few things). I really, really wish Julia did TRT as well. 🙂

MA

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