How do pointers work in Go and when should you pass by pointer vs by value?

Go is pass-by-value: every function argument is a copy. For types that are large or need to be mutated by the called function, passing a pointer avoids the copy and allows in-place modification. Understanding when to use pointers is essential for both correctness and performance.

// Pass by VALUE — mutation inside the function is invisible to caller
func doubleValue(n int) { n *= 2 } // n is a copy
x := 5
doubleValue(x)
fmt.Println(x) // still 5

// Pass by POINTER — mutation is visible
func doublePtr(n *int) { *n *= 2 }
doublePtr(&x)
fmt.Println(x) // 10

// Large structs — avoid copying by passing pointer
type BigStruct struct { data [1024]byte }
func processValue(b BigStruct) {} // copies 1 KB every call
func processPtr(b *BigStruct) {}  // copies only 8 bytes (pointer)

// Value receiver vs pointer receiver on methods
type Counter struct{ count int }
func (c Counter)  Get()  int { return c.count }     // value receiver — copy
func (c *Counter) Inc()      { c.count++ }           // pointer receiver — mutates

c := Counter{}
c.Inc()              // Go automatically takes &c
fmt.Println(c.Get()) // 1

// Pointer vs nil — always check before dereferencing
var p *int
fmt.Println(p)   // 
// fmt.Println(*p) // PANIC: nil pointer dereference

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