operators for array-stores

[AlexandrHoroshih]

Discussed in #147

^{Originally posted by AlexandrHoroshih June 4, 2021}
At the moment there is no option in basic effector api to do something like call that event on every item from this array in store or in event payload

Idea is to create operator which is something like this:

sampleForEach({
  source: Store<T[]> | Event<T[]>,
  clock,
  target: Event<T> | Effect<T> // will be run for Every T from T[] in source
})

Live example:
https://share.effector.dev/vx6hm1il

Possible use case:

const runTransaction = createEvent<Transaction>()
const runTransactionGroup = createEvent<Transaction[]>()

sampleForEach({
  source: runTransactionGroup,
  target: runTransaction, // run all transactions from group one-by-one
})

runTransaction.watch(t => console.log('Handling transaction...', t)) // for example, we just logging all transactions

runTransaction({
  type: 'transactionType',
  body: 'Single',
})

runTransactionGroup([
  {
    type: 'transactionType',
    body: 'group1',
  },
  {
    type: 'transactionType',
    body: 'group2',
  },
  {
    type: 'transactionType',
    body: 'group3',
  },
])

// in logs:
Handling transaction... 
 {type: "transactionType", body: "Single"}

Handling transaction... 
 {type: "transactionType", body: "group1"}

Handling transaction... 
 {type: "transactionType", body: "group2"}

Handling transaction... 
 {type: "transactionType", body: "group3"}
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