I was wandering whether there is currently a way of representing C++ style static variables in Julia. I haven’t found out how and I think they are pretty useful - especially when dealing with lots of object instances that share updatable properties. C++ static keywords are used both within function…

You can use an inner constructor (eg in the example below, with validation): let counter = 0 global get_counter() = counter struct Foo x::Int function Foo(x) x > 0 || error("invalid x") counter += 1 new(x) end end end which w…

Hmm const not a stand-in for C++ static. For a start something like this doesn’t work: const z = 0 function incrementZ() global z += 1 return end incrementZ() # WARNING: redefining constant z z # 1 incrementZ() z # 1 If I’m honest I don’t use const because I don’t really know how it works. Th…

The idiomatic answer to this is let, I believe: let z = 0 global function incrementZ() z += 1 return z end end println(incrementZ()) println(incrementZ())

Thanks. That certainly looks useful and the variable is encapsulated away. In the case of classes I guess I can do something like: mutable struct MyObject name::String age::Int64 end let population = 0 global function MakeMyObject(name::String, age::Int64) population += 1 return MyOb…

Awesome! :partying_face: I tried let ... global struct MyType ... end ... end and got an error so I assumed that you couldn’t have globally accessible structs inside the let block - but you’ve just shown that you can. Many thanks!

[image] Tamas_Papp: That said, global mutable state is difficult to reason about and may preclude some compiler optimizations, so it is generally avoided in Julia But the counter variable is not global, it’s in the let block so shouldn’t that be okay?

[image] Tamas_Papp: That said, global mutable state is difficult to reason about and may preclude some compiler optimizations, so it is generally avoided in Julia. Instead of porting code in C++ style, I would recommend finding another solution. const counter = Ref(0)

[image] ChrisRackauckas: const counter = Ref(0) yes but if do that you’ll keep getting warnings when you modify the reference. e.g. counter = Ref(1) # WARNING: redefining constant counter # Base.RefValue{Int64}(1) counter = Ref(2) # WARNING: redefining constant counter # Base.RefValue{Int6…

It is global to the type (in the sense that various instances share the value). If you absolutely need it, then go ahead and use this — but I think that mutable state is a bad habit, especially in Julia.

You do julia> const counter = Ref(1) Base.RefValue{Int64}(1) julia> counter[] = 2 2

[image] Tamas_Papp: It is global to the type (in the sense that various instances share the value). If you absolutely need it, then go ahead and use this — but I think that mutable state is a bad habit, especially in Julia. But the instances (of the objects) don’t actually share the value - …

Does Julia Need a C++ style `static` keyword?

Internals & Design

ChrisRackauckas September 26, 2019, 11:33am 9

const counter = Ref(0)

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Does Julia Need a C++ style `static` keyword?

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