Simple operators

• Operators are functions defined on publisher instances...
• ... each operator returns a new publisher ...
• ... operators can be chained to add processing steps

Example: map

• works like Swift's map
• ... operates on values over time

let publisher1 = PassthroughSubject<Int, Never>()

let publisher2 = publisher1.map { value in
	value + 100
}

let subscription1 = publisher1
	.sink { value in
		print("Subscription1 received integer: \(value)")
}

let subscription2 = publisher2
	.sink { value in
		print("Subscription2 received integer: \(value)")
}

print("* Demonstrating map operator")
print("Publisher1 emits 28")
publisher1.send(28)

print("Publisher1 emits 50")
publisher1.send(50)

subscription1.cancel()
subscription2.cancel()

Example: filter

• works like Swift's filter
• ... operates on values over time

let publisher3 = publisher1.filter {
	// only let even values pass through
	($0 % 2) == 0
}

let subscription3 = publisher3
	.sink { value in
		print("Subscription3 received integer: \(value)")
}

print("\n* Demonstrating filter operator")
print("Publisher1 emits 14")
publisher1.send(14)

print("Publisher1 emits 15")
publisher1.send(15)

print("Publisher1 emits 16")
publisher1.send(16)

本小节介绍的操作符map与filter，数据转换与过滤