Open Radar

 
Summary:
There is a case when function that accepts UnsafeMutablePointer can change value of immutable variable declared with let. The following code will compile and run successfully. It will show 2 and 3.

func bug(x: UnsafeMutablePointer<Int>) {
    x.memory += 1
}

func test() {
    let x: Int
    x = 1
    bug(&x)
    print(x)
    bug(&x)
    print(x)
}

Nothing must be able to change value of let, so I consider this behavior as bug.

To compare, if you'll try to assign 'x = 2' after 'x = 1' line, compilation will fail with "Immutable value 'x' may only be initialized once". But for some reason calling 'bug(&x)' is allowed to mutate immutable value.

Also, the strange thing is if I replace two lines 'let x: Int' and 'x = 1' by 'let x: Int = 1', compilation also fails with "Cannot pass immutable value as inout argument: 'x' is a 'let' constant" on lines where 'bug(&x)' is called. This is correct behavior, and the same error message should appear in the very first case.

Steps to Reproduce:
1. Install Xcode 7.0b6 (7A192o).
2. Create a playground for iOS, paste my code snippet in playground. Code compiles successfully.
3. Look at output: "2\n" and "3\n" are printed.

Expected Results:
Compilation error should occur. It should be "Cannot pass immutable value as inout argument: 'x' is a 'let' constant" on lines where 'bug(&x)' is called.

Actual Results:
Code compiles fine, immutable value is changed after its initialization.

Version:
Xcode 7.0b6 (7A192o), OS X 10.10.5.

Notes:


Configuration:
Swift 2.0, Xcode 7.0b6 (7A192o), OS X 10.10.5, building for iOS 9.0.

Attachments: