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PASS BY VALUE

Core Concept: Go always passes arguments by value - copies are made of all parameters, including pointers.

Why It Matters​

Explains why modifying parameters doesn't affect original values unless using pointers. Critical for understanding pointers.

When to Use​

This is not a pattern to "use" - it's how Go always works. You choose whether to pass values or pointers based on whether you need mutation.

Key Distinction​

Pass value:

func increment(x int) {
    x = x + 1  // Modifies copy, not original
}

a := 5
increment(a)
fmt.Println(a)  // Still 5

Pass pointer (pointer value is copied, but points to same address):

func increment(x *int) {
    *x = *x + 1  // Dereferences and modifies original
}

b := 5
increment(&b)
fmt.Println(b)  // Now 6

vs Java References​

JavaGo
Objects passed by referenceEverything passed by value
Primitives passed by valuePointers passed by value (address copied)
No pointer syntaxExplicit & and *

Trade-offs​

Pros: Predictable, no hidden side effects, explicit mutation
Cons: Large structs can be expensive to copy

This is why pointers are necessary - to pass the address (by value) instead of copying large data.

Quick Reference​

// Value passed - copy made
func modifyValue(s MyStruct) {
    s.Field = "changed"  // Changes copy only
}

// Pointer passed - address copied, data accessible
func modifyPointer(s *MyStruct) {
    s.Field = "changed"  // Changes original
}

// Even the pointer itself is copied!
func reassignPointer(p *int) {
    newVal := 100
    p = &newVal  // Only changes local copy of pointer
}

Key insight: When you pass a pointer, the address is copied, but both the original and copy point to the same memory location.

References​