Read a pointer, or fall back

Goal

Fill in ReadOrFallback so it returns the value p points to, or fallback when p is nil.

Example

x := 7
fmt.Println(ReadOrFallback(&x, -1)) // 7

var missing *int
fmt.Println(ReadOrFallback(missing, -1)) // -1

Rules

• Edit readorfallback.go. The function has a // TODO comment and a return line you will change.
• Check p against nil before dereferencing it.
• p pointing at 0 is not the same thing as p being nil — a pointer to 0 is still a real pointer, and should return 0, not fallback.
• Do not change the line func ReadOrFallback(p *int, fallback int) int {. Do not add imports.

What you'll practice

Guarding a pointer with a nil check before dereferencing it, and telling "no value" (nil) apart from "a value that happens to be zero."

Run it

gonomicon fetch week-1/13-03-read-or-fallback
cd 13-03-read-or-fallback
gonomicon test
gonomicon submit

Hints

1. Start by checking p against nil, the same way you'd guard any pointer before dereferencing it.
2. When p is nil there's nothing to read, so return fallback right away with an early return. Otherwise dereference p and return that.
3. if p == nil { return fallback } return *p