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malcommac/Hydra_Internals_12.swift

Created February 4, 2017 11:17
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Hydra_Internals_12.swift
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Hydra_Internals_12.swift
public func map_series<A, B, S: Sequence>(context: Context, items: S, transform: @escaping (A) throws -> Promise<B>) -> Promise<[B]> where S.Iterator.Element == A {
let initial = Promise<[B]>(resolved: [])
return items.reduce(initial) { chain, item in
return chain.then(in: context) { results in
try transform(item).then(in: context) { results + [$0] }
}
}
}
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