Claim (false): Julia isn't multiple dispatch but overloading

[Liso]

@ffevotte

the magic about Julia is the compiler’s ability to generate optimized code for all specialized versions of a method. This happens all the time, is key in how Julia operates and achieves performance, and I don’t have much difficulty explaining the benefit of this.

I am probably missing something. How could permanent runtime type check (and runtime method selection) help to achieve better performance?