ExpressionTrait.java

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

import org.apache.doris.nereids.annotation.Developing;
import org.apache.doris.nereids.exceptions.UnboundException;
import org.apache.doris.nereids.trees.TreeNode;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.Variable;
import org.apache.doris.nereids.types.DataType;

import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * ExpressionTrait.
 */
public interface ExpressionTrait extends TreeNode<Expression> {

    boolean nullable();

    default boolean notNullable() {
        return !nullable();
    }

    // check legality before do type coercion.
    // maybe we should merge checkInputDataTypes and checkLegality later.
    @Developing
    default void checkLegalityBeforeTypeCoercion() {}

    @Developing
    default void checkLegalityAfterRewrite() {}

    /**
     * getArguments.
     */
    default List<Expression> getArguments() {
        boolean hasVariableArg = false;
        for (Expression arg : children()) {
            if (arg instanceof Variable) {
                hasVariableArg = true;
                break;
            }
        }
        if (hasVariableArg) {
            ImmutableList.Builder<Expression> arguments = ImmutableList.builder();
            for (Expression arg : children()) {
                if (arg instanceof Variable) {
                    arguments.add(((Variable) arg).getRealExpression());
                } else {
                    arguments.add(arg);
                }
            }
            return arguments.build();
        } else {
            return children();
        }
    }

    /**
     * getArgument.
     */
    default Expression getArgument(int index) {
        Expression arg = child(index);
        if (arg instanceof Variable) {
            return ((Variable) arg).getRealExpression();
        } else {
            return arg;
        }
    }

    default List<DataType> getArgumentsTypes() {
        return getArguments()
                .stream()
                .map(Expression::getDataType)
                .collect(ImmutableList.toImmutableList());
    }

    default DataType getArgumentType(int index) {
        return child(index).getDataType();
    }

    default DataType getDataType() throws UnboundException {
        throw new UnboundException(toSql() + ".getDataType()");
    }

    default String toSql() throws UnboundException {
        throw new UnboundException("sql");
    }

    /**
     * foldable() mainly use in fold expression. Udf and UniqueFunction are not foldable.
     * But if want to check an expression contains non-idempotent, such as `rand()`, `uuid()`, etc.,
     * you should use Expression::containsUniqueFunction instead.
     */
    default boolean foldable() {
        return true;
    }

    /**
     * Identify the expression itself is deterministic or not, default true
     */
    default boolean isDeterministic() {
        return true;
    }

    /**
     * Identify the expression is containing non-deterministic expr or not
     */
    default boolean containsNondeterministic() {
        return anyMatch(expr -> !((ExpressionTrait) expr).isDeterministic());
    }
}