Swift comes with some implicitly defined variables – that are variables that are accessible in your code even though you’ve not explicitly defined them. These variables are helpful when logging errors or writing test code.
- __COLUMN__ (Int): The column number in the source file on which the currently executing code appears
- __FILE__ (String): The filename of the file in which the currently executing code appears
- __FUNCTION__ (String): The name of the declaration in which the currently executing code appears
- __LINE__ (Int): The line number in the source file on which the currently executing code appears
- C_ARGC (CInt): The number of command line arguments passed to the executable
- C_ARGV (UnsafePointer<CString>) (appears not to be available in playgrounds?): The command line arguments passed to the executable, C_ARGV[0] is the first argument, C_ARGV[1] is the second argument, etc.
