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[SR-3316] "Script mode" globals have internal visibility and can be accessed before initialization from other files #45904

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jckarter opened this issue Dec 2, 2016 · 0 comments
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bug A deviation from expected or documented behavior Compiler StarterProposal

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jckarter commented Dec 2, 2016

Previous ID SR-3316
Radar None
Original Reporter @jckarter
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, StarterProposal
Assignee None
Priority Medium

md5: e092a51eda538e02ab484391d0b1b1a5

Issue Description:

Variables declared in a script default to internal visibility, like other global declarations, but this is problematic, because semantically they behave more like local variables. Another file can access the global before its initializer has even run:

// main.swift
class C {}
var x: C
foo()
x = C()
// foo.swift
func foo() {
  print(x) // loads garbage from `x` from main.swift
}

In a future version of Swift, script globals should be changed to be private by default. We could possibly also allow a script global to be declared with explicit access control, which would make it visible to other files but would also have to make the variable behave more like a library global, with a dispatch_once-d initializer, e.g.:

// main.swift
var x = 42 // private, eagerly initialized
private var y = 17 // private, initialized on demand
internal var z = 38 // internal, initialized on demand
@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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Labels
bug A deviation from expected or documented behavior Compiler StarterProposal
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