Multi-stream: Map.of refuses the duplicates a real feed contains

Map.of is a fine literal and a poor loader. It throws on a duplicate key and on a null value, which a feed produces on its first bad day. toMap with a merge function is the version that survives contact with data.

• Multi-stream: a record with a mutable component is a broken Map key
• Multi-stream: an unmodifiable view is not a snapshot of the feed
• Multi-stream: toMap's merge function runs only on a collision
• Multi-stream: nothing runs until the terminal operation
• Multi-stream: indexing the other side costs memory a sorted merge does not
• Multi-stream: UNORDERED is a promise you make, not one you receive

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Published 2026-09-20

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