poi/src/java/org/apache/poi/ss/formula/functions/ArrayFunction.java

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   this work for additional information regarding copyright ownership.
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package org.apache.poi.ss.formula.functions;

import org.apache.poi.ss.formula.eval.BlankEval;
import org.apache.poi.ss.formula.eval.ErrorEval;
import org.apache.poi.ss.formula.eval.MissingArgEval;
import org.apache.poi.ss.formula.eval.ValueEval;

/**
 * @author Robert Hulbert
 * Common Interface for any excel built-in function that has implemented array formula functionality.
 */

public interface ArrayFunction {
    
    /**
     * @param args the evaluated function arguments.  Empty values are represented with
     * {@link BlankEval} or {@link MissingArgEval}, never <code>null</code>.
     * @param srcRowIndex row index of the cell containing the formula under evaluation
     * @param srcColumnIndex column index of the cell containing the formula under evaluation
     * @return The evaluated result, possibly an {@link ErrorEval}, never <code>null</code>.
     * <b>Note</b> - Excel uses the error code <i>#NUM!</i> instead of IEEE <i>NaN</i>, so when
     * numeric functions evaluate to {@link Double#NaN} be sure to translate the result to {@link
     * ErrorEval#NUM_ERROR}.
     */

    ValueEval evaluateArray(ValueEval[] args, int srcRowIndex, int srcColumnIndex);
}