struct SourceCodeContext {
    let file: String
    let line: Int
    let function: String

    init(_ file: String = #file, _ line: Int = #line, _ function: String = #function) {
        self.file = file
        self.line = line
        self.function = function
    }
}

struct SomeError: Error {
    let context: SourceCodeContext

    init(_ context: SourceCodeContext = SourceCodeContext()) {
        self.context = context
    }
}

let error = SomeError()
error.context.line /// expected 25, but has initializer line value - 21
error.context.function /// `init` value