What do the parentheses before the function name mean in Go?

Hi everyone! I recently started learning Go and the function declaration syntax is very confusing to me. I'm used to Python where everything is simple: `def func_name(args):`. But in Go I see strange constructs. For example, I came across this code: ```go type Rectangle struct { Width float64 Height float64 } func (r Rectangle) Area() float64 { return r.Width * r.Height } ``` What is this `(r Rectangle)` before the function name `Area`? I thought parameters were written in parentheses after the function name, like in other languages. But here they are somehow before the name. Is this some special syntax? I tried writing just `func Area(r Rectangle) float64` — it works, but then I can't call the method as `rect.Area()`, only as `Area(rect)`. What's the difference? When should I use