string file = __FILE__ considered harmful (and solution)

[Walter Bright]

On 5/30/2018 1:27 AM, FeepingCreature wrote:
> There's a very common idiom where in order to report line numbers of an error or 
> a log line at the callsite of a function, you pass __FILE__ and __LINE__ as 
> default parameters:
> 
> void foo(string file = __FILE__, size_t line = __LINE__);
> 
> What's wrong with this?
> 
> Say you add a string parameter, such as
> 
> void foo(string msg, string file = __FILE__, size_t line = __LINE__);
> 
> foo("Hello World");
> 
> Now when you accidentally grab an old version of the library, your new code will 
> still run, but it will believe that it's being called from file "Hello World", 
> line 15.

A solution:

   enum E { reserved }

   void foo(E e = E.reserved, string file = __FILE__, size_t line = __LINE__);
   void foo(string msg, E e = E.reserved, string file = __FILE__, size_t line = 
__LINE__);