# OOP-brained design patterns

**URL:** <https://discourse.julialang.org/t/oop-brained-design-patterns/135423>\
**Category:** General Usage\
**Created:** [February 3, 2026, 12:03pm UTC](https://discourse.julialang.org/t/oop-brained-design-patterns/135423 "2026-02-03T12:03:29Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![PatrickHaecker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/patrickhaecker/32/222891_2.png) [@PatrickHaecker](https://discourse.julialang.org/u/PatrickHaecker)\
**Post date:** [June 11, 2026, 5:35am UTC](https://discourse.julialang.org/t/oop-brained-design-patterns/135423/4 "2026-06-11T05:35:08Z")

</div>

This is an interesting pattern which leads to very efficient code. However, the readability is not so great.

What I use in these cases:

- Always introduce an abstract type per concrete type, at least for types which are public. For `MyType` this would be `AMyType` (because it is _a_ `MyType` in the sense of “I don’t care which one” – interestingly, this implies the same meaning as `AbstractMyType` or `AnyMyType`, but is shorter and simpler to read after getting used to)
- Use the concrete type in the field constraints of your structs (obviously).
- Never type-constraint your methods to the concrete type, but to the abstract type.
- If you want to extend a type, it’s then simply introducing another abstract type (to again be reusable) and letting a macro from one of the packages copy over the fields into a new type.

No downsides of this procedure have been identified [when I asked here](https://discourse.julialang.org/t/only-abstract-types-in-method-signatures/125435).  
One day I should probably create a package for this so that you could e.g. write

```julia
@extendable struct Base
    baseField::Int
end

function do_something(base::ABase)
    base.baseField
end

```

and it would just work. Or even better

```julia
using ExtendableModules

@extendable module MyModule
struct Base
    baseField::Int
end

function do_something(base::Base)
    base.baseField
end
end

```

where the macro would rewrite all `struct`s in the module to define their abstract type, too. Additionally, it would rewrite all method type constraints to use the abstract types. That would be nice.

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_[View the full topic](https://discourse.julialang.org/t/oop-brained-design-patterns/135423)._