What's the best practice to use Global variable vs static local variable

Using Swift
1

We have a discussion about when to use a global variable or local variable but didn't come to a specific conclusion. Is there any guidance or best practice to choose when to use a global or local static variable?

Such as

let sharedTest = Test()

class Test {
    static let shared = Test()
}
2

@Joe_Groff @John_McCall Hey sorry to @ you, maybe it's too simple for you to answer, but I did search on the network and checked the docs of swift and didn't find any useful information.

3

They are identical from an implementation standpoint. It's really up to your judgment whether a global property should be scoped to the module or is related to a specific type.

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4

Sometime you have no choice:

struct Foo<T> {
    static var x = 1    // error: static stored properties not supported in generic types
    // this is okay but it's evaluated on every access
    static var x: Int { 1 }
}
1 Like
5

That's a good example!

6

To be clear, if that were supported, it would have different semantics from declaring it at the top level, because you’d have a different variable for each set of generic arguments.

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7

I for one would very much like this feature.

I would use it when writing a mathematical function that’s generic over one of the numeric protocols, and which involves caching previously-computed values.

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