Strange Go syntax: what do the parentheses before the function name mean?

Hello everyone! I just started learning Go after Python and JavaScript, and I'm confused by one syntax feature. In code, I often see something like this: ```go type Rectangle struct { Width float64 Height float64 } func (r Rectangle) Area() float64 { return r.Width * r.Height } ``` Why are there parentheses with `(r Rectangle)` before the function name `Area`? In Python, I would just write `def area(self):`. I understand it has something to do with struct methods, but I can't grasp the logic. Here's another example that confused me: ```go func (p *Person) SetName(name string) { p.Name = name } ``` Why sometimes they write `(p *Person)` and sometimes `(p Person)`? And what happens if I remove these parentheses altogether? For example: ```go func Area() float64 { return 0 } ``` Is this