Double through a pointer

Goal

Fill in DoubleThroughPointer so it doubles the int that n points to, writing the result back through the pointer — and does nothing if n is nil.

Example

value := 7
DoubleThroughPointer(&value)
fmt.Println(value) // 14

value = -3
DoubleThroughPointer(&value)
fmt.Println(value) // -6

var missing *int
DoubleThroughPointer(missing) // does nothing, does not panic

Rules

• Edit double.go. The function has a // TODO comment and currently does nothing.
• Use *n to read and write the value n points to.
• If n is nil, the function should do nothing: no panic, no change to anything.
• Do not change the line func DoubleThroughPointer(n *int) {. Do not add imports.

What you'll practice

Dereferencing a pointer to read and write a value, writing into a caller's variable through a pointer parameter, and checking a pointer against nil before using it.

Run it

gonomicon fetch week-1/13-01-double-through-a-pointer
cd 13-01-double-through-a-pointer
gonomicon test
gonomicon submit

Hints

1. n is a *int, so you reach the value it points to with *n. Doubling means adding that value to itself, or multiplying it by 2.
2. Check n against nil before touching *n — dereferencing a nil pointer panics. If n is nil, just return without doing anything.
3. if n == nil { return } *n = *n + *n