I am following a Go tutorial and am stuck as I cant understand a particular method signature:
func (p *Page) save() error {
filename := p.Title + ".txt"
return ioutil.WriteFile(filename, p.Body, 0600)
}
The docs explain this as follows:
This method's signature reads: "This is a method named save that takes as its receiver p, a pointer to Page . It takes no parameters, and returns a value of type error."
I cant understand what the receiver is. I would read this as it being a parameter but then I would expect a parameter to be in save().
The receiver is the object on what you declare your method.
When want to add a method to an object, you use this syntax.
The receiver is just a special case of a parameter. Go provides syntactic sugar to attach methods to types by declaring the first parameter as a receiver.
For instance:
func (p *Page) save() error
reads "attach a method called save that returns an error to the type *Page", as opposed to declaring:
func save(p *Page) error
that would read "declare a function called save that takes one parameter of type *Page and returns an error"
As proof that it's only syntactic sugar you can try out the following code:
p := new(Page)
p.save()
(*Page).save(p)
Both last lines represent exactly the same method call.
Also, read this answer.