Merge multiple sources.
def mergeLatest[U >: Out, M](that: Graph[SourceShape[U], M], eagerComplete: Boolean = false): Repr[immutable.Seq[U]] def mergeLatestMat[U >: Out, Mat2, Mat3](that: Graph[SourceShape[U], Mat2], eagerClose: Boolean)(matF: (Mat, Mat2) => Mat3): ReprMat[immutable.Seq[U], Mat3]
MergeLatest joins elements from N input streams into stream of lists of size N. i-th element in list is the latest emitted element from i-th input stream. MergeLatest emits list for each element emitted from some input stream, but only after each input stream emitted at least one element
emits when element is available from some input and each input emits at least one element from stream start
completes all upstreams complete (eagerClose=false) or one upstream completes (eagerClose=true)