OR-5261 Combining Operators:: switchToLatest()

[crazymanish]

Context

• Close ticket: [w23(4june-10june)] Operators:: Combining Operators: Combining #24

Operators are publishers

• In Combine, methods that perform an operation on values coming from a publisher are called operators.
• Each Combine operator actually returns a publisher. Generally speaking, that publisher receives the upstream values, manipulates the data, and then sends that data downstream.

In this PR

• Combining Operators:: switchToLatest()
• switchToLatest() Republishes elements sent by the most recently received publisher.
• https://developer.apple.com/documentation/combine/publishers/reduce/switchtolatest()
• This operator works with an upstream publisher of publishers, flattening the stream of elements to appear as if they were coming from a single stream of elements. It switches the inner publisher as new ones arrive but keeps the outer publisher constant for downstream subscribers.
• When this operator receives a new publisher from the upstream publisher, it cancels its previous subscription. Use this feature to prevent earlier publishers from performing unnecessary work, such as creating network request publishers from frequently updating user interface publishers.

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• If you’re not sure why this is useful in a real-life app, consider the following scenario:
• Your user taps a button that triggers a network request. Immediately afterward, the user taps the button again, which triggers a second network request. But how do you get rid of the pending request, and only use the latest request? switchToLatest to the rescue!