static Function < Optional < Descriptor > , String > concat ( final Function < ? super Optional < Descriptor > , String > function1 , final Function < ? super Optional < Descriptor > , String > function2 ) { return new Function < Optional < Descriptor > , String > ( ) { @ Override public String apply ( Optional < Descriptor > optDescriptor ) { return function1 . apply ( optDescriptor ) + function2 . apply ( optDescriptor ) ; } } ; }
Returns a function which concatenates the outputs of the two input functions .