Detect the bug in the following code

[Brian Schott via Digitalmars-d]

On Thursday, 16 April 2015 at 22:48:53 UTC, Idan Arye wrote:
> "%s %s".writefln = ("foo".tuple = "bar").expand;

Please make a pull request: 
https://github.com/Hackerpilot/Idiotmatic-D