Swift assert anyway to print variables in string

Question

Background: In Objective-C, I would create my assertion with debug information included:

NSAssert(poetCount > 5, "Expected poetCount > 5; Actual: %d", poetCount);

However, the global assert function in Swift doesn't seem to allow this, because the message parameter is a StaticString. So I can NOT do this:

assert(NSFileManager.defaultManager().fileExistsAtPath(fullpath), 
"Expected: File to Exist @ \(fullpath)")

Question: Is there an alternative assert function that does not require a static string, or should I continue using NSAssert if I want to put in extra information to make debugging easier?

Answer 1

I don't think you can currently because of the StaticString param. I tried setting the message string with a let but you can't even put a variable in there it seems. It has to be a StaticString in quotes.

For what it's worth, Apple's sample code follows the same pattern:

assert(listItems && listItems!.count == 1, "There must be exactly one moved item.")

Answer 2

You can write your own version of assert with String. Here is example:

func assert(condition: @autoclosure () -> Bool, _ message: String = "") {
    #if DEBUG
        if !condition() {
            println(message);
                abort()
        }
    #endif 
}

or with additional debug info:

func assert(condition: @autoclosure () -> Bool, _ message: String = "", file: String = __FILE__, line: Int = __LINE__) {
    #if DEBUG
        if !condition() {
            println("assertion failed at \(file):\(line): \(message)");
                abort()
        }
    #endif
}