Essentially without generics, any kind of polymorphic code needs to use dynamic dispatch. For example, if you add a generic sort() function for collections, you

Essentially without generics, any kind of polymorphic code needs to use dynamic dispatch. For example, if you add a generic sort() function for collections, you would need to lookup the comparison function for any arguments at runtime. Generic programming - be it through type parameters, ad hoc polymorphism, or whatever - allows a language implementation to know what that comparison function is at compile time and inline it accordingly. This is true for all kinds of things you may want to do generically. Sorting, layout of objects, iteration, etc. Ultimately generic typing is a way of better expressing the constraints of a program to a compiler, which means the compiler can do a better job of generating code for specific instances. The downside is that the compiler needs to generate code explicitly for each concrete instance of a generic function or type, which means that it takes more compile time and code size is larger. Edit: I'd also like to point out that JIT compilers and sufficiently-smart AOT compilers can do this sort of inlining if they can prove that for any combination of run time types passed into a sort() they have the same comparison function and inline it as needed. That said it's the same (or higher) complexity as a generics system, with more pitfalls (for example, if they can't prove it but make a guess the sort function never changes, then get the guess wrong, they have to de-optimize).