swiftlang/swift
Ver no GitHub[SR-3316] "Script mode" globals have internal visibility and can be accessed before initialization from other files
Open
#45.904 aberto em 2 de dez. de 2016
access controlcompilergood first issuescript modeswift evolution proposal needed
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Description
| Previous ID | SR-3316 |
| Radar | None |
| Original Reporter | @jckarter |
| Type | Bug |
| 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