Additional examples to single update function with upsert functionality

[malthe]

Under "Why not have a single function that updates the value if no if the key is mapped?", instead of using a try/finally clause, we could write:

counts.emplace(key, (existing) => existing ?? 0 + 1)

Factory with just insertion:

counts.emplace(key, (existing) => existing ?? someFactory());

Insertion and update, assuming the created value here is always truthy, a reasonable assumption.

counts.emplace(key, (existing) => existing && doSomething(existing) || someFactory())

I don't think these examples are adequately presented in the proposal.

[dminor]

The new direction for the proposal is only looking at the insert use case, not updates.