void bothAandB(String dimName) {
            if (dimName.equals(concatDimension)) {
                splitInfoA.handleDims.add(DimType.concat);
                splitInfoB.handleDims.add(DimType.concat);
                combineHow.add(CombineHow.concat);
            } else {
                splitInfoA.handleDims.add(DimType.common);
                splitInfoB.handleDims.add(DimType.common);
                combineHow.add(CombineHow.both);
            }
        }
Maps the content in the given list to the given array, using the given index map.

@return true if the mapping was successful, false if one of the destination positions was
        occupied by a different value
vespajlib/src/main/java/com/yahoo/tensor/functions/Concat.java