69 lines
2.0 KiB
Go
69 lines
2.0 KiB
Go
// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import "fmt"
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func main() {
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var (
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counter int
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V int
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P *int
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)
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counter = 100 // counter is an int variable
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P = &counter // P is a pointer int variable
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V = *P // V is a int variable (a copy of counter)
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if P == nil {
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fmt.Printf("P is nil and its address is %p\n", P)
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}
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if P == &counter {
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fmt.Printf("P is equal to counter's address: %p == %p\n",
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P, &counter)
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}
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fmt.Printf("counter: %-13d addr: %-13p\n", counter, &counter)
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fmt.Printf("P : %-13p addr: %-13p *P: %-13d\n", P, &P, *P)
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fmt.Printf("V : %-13d addr: %-13p\n", V, &V)
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fmt.Println("\n••••• change counter")
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counter = 10 // V doesn't change because it's a copy
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fmt.Printf("counter: %-13d addr: %-13p\n", counter, &counter)
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fmt.Printf("V : %-13d addr: %-13p\n", V, &V)
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fmt.Println("\n••••• change counter in passVal()")
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counter = passVal(counter)
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fmt.Printf("counter: %-13d addr: %-13p\n", counter, &counter)
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fmt.Println("\n••••• change counter in passPtrVal()")
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passPtrVal(&counter) // same as passPtrVal(&counter) (no need to return)
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passPtrVal(&counter) // same as passPtrVal(&counter) (no need to return)
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fmt.Printf("counter: %-13d addr: %-13p\n", counter, &counter)
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}
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// *pn is a int pointer variable (copy of P)
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func passPtrVal(pn *int) {
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fmt.Printf("pn : %-13p addr: %-13p *pn: %d\n", pn, &pn, *pn)
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// pointers can breach function isolation borders
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*pn++ // counter changes because `pn` points to `counter` — (*pn)++
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fmt.Printf("pn : %-13p addr: %-13p *pn: %d\n", pn, &pn, *pn)
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// setting it to nil doesn't effect the caller (the main function)
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pn = nil
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}
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// n is a int variable (copy of counter)
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func passVal(n int) int {
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n = 50 // counter doesn't change because `n` is a copy
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fmt.Printf("n : %-13d addr: %-13p\n", n, &n)
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return n
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}
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