Range loops

Canonical guidance

• range gives you a copy of the element value
• mutate by index when the collection itself must change
• remember the ranged expression is evaluated once up front

Use when

• read-only iteration
• concise loops over slices, maps, strings, and channels
• index plus value traversal

Avoid

• editing struct elements through the copied loop variable
• taking addresses of loop variables when element identity matters
• assuming appends change what a slice range will visit

Preferred pattern

for i := range users {
	users[i].Active = true
}

Anti-pattern

• writing to fields on the ranged value and expecting the original slice element to change

Explanation: This anti-pattern is tempting because the loop variable looks like the element, but for most ranges it is just a copy of that value.

Why

• range loops are concise, but their value-copy semantics matter for correctness