As the name implies, single dispatch is just a special case of multiple dispatch. Everything that can be done with single dispatch works exactly the same (arg1.

As the name implies, single dispatch is just a special case of multiple dispatch. Everything that can be done with single dispatch works exactly the same (arg1.f(arg2...) is just f(arg1, arg2...) in Julia), so there is no loss in expressivity. The only conceptual difference in multiple dispatch is that arg1 is not considered special, which makes sense for a scientific language as for example in 1 + 5 the operator '+' isn't really owned by the "object" 1, it's a property of the whole formula (the combination of the operator itself and all operands). And the consequence in terms of programming is exactly that it that it shifts the responsibility of handling interoperability to whoever creates a new type. For example if I create MyType and want a method SomeoneType + MyType to work, I don't need to change the '+' implementation on SomeoneType for that to work (for example making a PR on his library), I only define methods with the type I just created. Which is why people say Julia ecosystem compose a lot, the creator of SomeoneType can just focus on what he wants and possibly never even know about MyType, MyType will extend it with whatever I want without having to re-implement stuff that SomeoneType already implemented (only MyType stuff and the intersection between libraries, defined by methods that use MyType and SomeoneType), and the final user can just import all stuff he wants and have a library that looks like a monolith but is actually many smaller libraries working together this way.