Swift: Reduce with closure -

code:

     var treasures: [treasure] = []       treasures = [treasurea, treasureb, treasurec, treasured, treasuree]       let recttodisplay = self.treasures.reduce(mkmaprectnull) {         (maprect: mkmaprect, treasure: treasure) -> mkmaprect in         // 2         let treasurepointrect = mkmaprect(origin: treasure.location.mappoint, size: mkmapsize(width: 0, height: 0))         // 3         return mkmaprectunion(maprect, treasurepointrect)     } 

in code above, running reduce function on treasures array, 2 parameters passed in closure: (maprect: mkmaprect, treasure: treasure). how closure know second parameter element treasures array , first parameter result of closure returns?

is default second parameter passed in closure element array that's executing reduce function?

swift's array class has definition of reduce looks this:

func reduce<t>(initial: t, fn: (t, t) -> t) -> t {     var val = initial     e in self {         val = fn(val, e)     }     return e } 

that say, definition of reduce dictates order in parameters passed closure provide.

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^{note actual definition of swift's reduce more complicated 1 provided above, example above basic gist.}