A short way to see it for me is to reason in terms of capabilities.
What is an instance of a given type supposed to be able to do? (method)
versus what am I able to do with or upon a given instance (function).
It's not always clear though but it can help.
On Thursday, June 2, 2022 at 4:38:37 PM UTC+2 h...@deividaspetraitis.lt
wrote:
> Background: when I am writing code mostly I end up with some clunky
> solutions I am not happy with and one of the reasons I think is that I
> might be mixing funcs vs methods.
>
> So the question is basically the title.
>
> I have searched both in this group ( without a luck ) and in the Internet
> for possible ideas/answers and I end up with following points:
>
> 1. Structs are for representing things, they are things
> 2. Funcs are for performing actions, calculating things
> 3. Methods for performing actions on thing state
> 4. Methods to satisfy interface
>
> Based on these points, let's have a "thing":
>
> ```
> type Person struct {
> weight float32 // pounds
> height float32 // inches
> }
> ```
>
> And calculate BMI:
>
> ```
> func CalculateBMI(weight float32 height float32) float32 {
> return weight / (height * height) x 703
> }
>
> p := Person{157, 66}
>
> CalculateBMI(p.weight, p.height)
> ```
>
> However if I would want for example to implement some kind of interface I
> would be forced to use method over func, but it looks weird to me for some
> reason:
>
> ```
> interface BMICalculator {
> CalculateBMI() float32
> }
>
> // Satisfies BMICalculator
> func (p * Person) CalculateBMI() float32 {
> return p.weight / (p.height * p.height) x 703
> }
> ```
>
> For example when looking at this STD code I am not longer to reason about
> choices funcs vs methods based on points above:
> https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;l=26;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708
>
> Why `(a
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708;bpv=1;bpt=1;l=26?gsn=a&gs=kythe%3A%2F%2Fgo.googlesource.com%2Fgo%3Flang%3Dgo%3Fpath%3Dnet%23param%2520TCPAddr.family%253Aa>
> *TCPAddr
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=21>
> ) family
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708;bpv=1;bpt=1;l=26?gsn=family&gs=kythe%3A%2F%2Fgo.googlesource.com%2Fgo%3Flang%3Dgo%3Fpath%3Dnet%23method%2520TCPAddr.family>()`
>
> is implemented as a method when it can be implemented as pure func like:
>
> ```
> func Family
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708;bpv=1;bpt=1;l=26?gsn=family&gs=kythe%3A%2F%2Fgo.googlesource.com%2Fgo%3Flang%3Dgo%3Fpath%3Dnet%23method%2520TCPAddr.family>
> (a
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708;bpv=1;bpt=1;l=26?gsn=a&gs=kythe%3A%2F%2Fgo.googlesource.com%2Fgo%3Flang%3Dgo%3Fpath%3Dnet%23param%2520TCPAddr.family%253Aa>
> *TCPAddr
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=21>)
>
> int
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=8a56c7742d96c8ef8e8dcecaf3d1c0e9f022f708;bpv=1;bpt=1;l=26?gsn=int&gs=kythe%3A%2F%2Fgo.googlesource.com%2Fgo%3Flang%3Dgo%23int%2523builtin>
>
> {
> if a
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=26>
>
> == nil || len(a
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=26>
> .IP
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=22>)
>
> <= IPv4len
> <https://cs.opensource.google/go/go/+/master:src/net/ip.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=22>
>
> {
> return syscall <http://godoc.org/syscall>.AF_INET
> <https://cs.opensource.google/go/go/+/master:src/syscall/zerrors_linux_amd64.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=26>
>
> }
> if a
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock_posix.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=26>
> .IP
> <https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=22>
> .To4
> <https://cs.opensource.google/go/go/+/master:src/net/ip.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=211>()
>
> != nil {
> return syscall <http://godoc.org/syscall>.AF_INET
> <https://cs.opensource.google/go/go/+/master:src/syscall/zerrors_linux_amd64.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=26>
>
> }
> return syscall <http://godoc.org/syscall>.AF_INET6
> <https://cs.opensource.google/go/go/+/master:src/syscall/zerrors_linux_amd64.go;drc=46ab7a5c4f80d912f25b6b3e1044282a2a79df8b;l=27>
>
> }
> ```
>
> So using reasoning above based on silly example looks O.K. but I seems
> that I might be still missing some kind of context/information because I
> can't explain example from STD.
>
> I would like to see what other people approaches this "problem" and to
> learn is there any other rules/guidelines to follow.
>
> Cheers, Deividas
>
>
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