Whats the difference of functions and methods in Go?

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As far as I understand at the moment: functions are “global”, which means I do not have to import a package to use functions, they are always there. Methods are bound to packages. Is this correct?

No, that’s not correct. There are just a couple of functions from the builtin package which are always available. Everything else needs to be imported.

The term “method” came up with object-oriented programming. In an OOP language (like C++ for example) you can define a “class” which encapsulates data and functions which belong together. Those functions inside a class are called “methods” and you need an instance of that class to call such a method.

In Go, the terminology is basically the same, although Go isn’t an OOP language in the classical meaning. In Go, a function which takes a receiver is usually called a method (probably just because people are still used to the terminology of OOP).

So, for example:

func MyFunction(a, b int) int {
  return a + b
}
// Usage:
// MyFunction(1, 2)

but

type MyInteger int
func (a MyInteger) MyMethod(b int) int {
  return a + b
}
// Usage:
// var x MyInteger = 1
// x.MyMethod(2)

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