map과 filter로 변환하기

Between a publisher and its subscriber you can insert operators that transform values as they flow downstream.

The map operator runs a closure on every value and emits the result, changing the stream's shape.

Because map returns whatever you want, the Output type can change, like turning numbers into strings.

The filter operator keeps only the values whose closure returns true and silently discards the rest.

Operators compose cleanly: chain filter then map to first narrow the stream, then reshape it.

Each operator sees only the output of the one above it, so reordering map and filter can quietly change your result.

Use compactMap when your transform may return nil, and Combine drops those empty results for you.

The removeDuplicates operator emits a value only when it differs from the previous one.

The scan operator carries a running result, emitting an updated total for every value, like a live sum.

Reading top to bottom, a pipeline tells a story: this is where the declarative power of operators shines.

Keep operator closures pure: avoid side effects so each value transforms predictably and tests stay simple.

You learned to reshape streams: map transforms, filter narrows, and compactMap clears out nil values. ✨