fill output range with result of fn() called per elements
import std.array; auto app = appender!(int[])(); mapFlat!(a=>to!int(a)*2)( app, [1,2], 3, [[4,5],[6]], iota(7,9), [[[9],[10,11]],[[12]]], Vec([13.3,666,105]) ); assertEq( app.data, [2,4,6,8,10,12,14,16,18,20,22,24,26,1332,210] );
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fill output range with result of fn() called per elements