Nullable.java

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package org.apache.doris.nereids.trees.expressions.functions.scalar;

import org.apache.doris.catalog.FunctionSignature;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.functions.AlwaysNullable;
import org.apache.doris.nereids.trees.expressions.functions.CustomSignature;
import org.apache.doris.nereids.trees.expressions.shape.UnaryExpression;
import org.apache.doris.nereids.types.DataType;

import com.google.common.base.Preconditions;

import java.util.List;

/**
 * change non_nullable input col to nullable col
 */
public class Nullable extends ScalarFunction implements UnaryExpression, CustomSignature, AlwaysNullable {

    public Nullable(Expression expr) {
        super("nullable", expr);
    }

    @Override
    public FunctionSignature customSignature() {
        DataType dataType = getArgument(0).getDataType();
        return FunctionSignature.ret(dataType).args(dataType);
    }

    @Override
    public Expression withChildren(List<Expression> children) {
        Preconditions.checkArgument(children.size() == 1,
                "the child expression of NonNullable should be only one");
        return new Nullable(children.get(0));
    }
}