debugging a struct implementing an increment function

Question

I’m trying to implement an increment function on my struct. I’m not sure why, but it appears that when I call F.incr() in main, the fib struct’s parameters appear to remain constant. I think I may have an incorrect idea about what I’m doing in my incr() function, though I’m not able to find the right documentation. What am I missing?

type fib struct { i uint64 fa uint64 fb uint64 } func (F fib) incr(){ F.i++ F.fa, F.fb = F.fa+F.fb, F.fa } func main() { F := fib{1,1,0} var sum uint64 = 0 for; F.i <= 10; F.incr() { k := f(F.i, F.fb, F.fa) fmt.Printf("calculating the %vth f(i,F_%v, F_%v): %v\n", F.i, F.i-1, F.i, k) —snip-

edit: thanks @peterSO, I needed to change incr to func (F *fib) incr(){

In Go, all arguments are passed by value. Pass a pointer. The documentation is The Go Programming Language Specification. For example, "the parameters of the call are passed by value to the function" golang.org/ref/spec#Calls — peterSO
– peterSO, Commented Feb 16, 2020 at 18:48
The code from the question does not compile, however as @peterSO wrote you need to use reference for incr() function. See here -> play.golang.org/p/g2iIXFY4y_U — Leron
– Leron, Commented Feb 16, 2020 at 18:52

automaticAllDramatic · Accepted Answer · 2020-02-16 20:09:33Z

You need to update your method to increase the value of the variable at the location. Hence, you need to change the F() method

func (F *fib) incr(){ F.i++ F.fa, F.fb = F.fa+F.fb, F.fa }

The difference being the *

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