First Or Default Null (ARCH5078)

Key go.performance.first-or-default-null · Severity warning · Category performance

Accessing [0] of a filtered slice without a length check panics when the result is empty. Add an emptiness guard before the access.

Incorrect

func firstAdmin(users []User) User {
  admins := filter(users, isAdmin)
  return admins[0]
}

Correct

func firstAdmin(users []User) (User, bool) {
  admins := filter(users, isAdmin)
  if len(admins) == 0 {
    return User{}, false
  }
  return admins[0], true
}

Fix

Add a len(...) == 0 check before accessing the first element.