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Enjoy is a simple, light, rapid, independent, extensible Java Template Engine.

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/**
 * Copyright (c) 2011-2019, James Zhan 詹波 ([email protected]).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.jfinal.template.expr.ast;

import java.util.ArrayList;
import java.util.List;
import com.jfinal.template.TemplateException;
import com.jfinal.template.stat.Scope;

/**
 * ExprList
 */
public class ExprList extends Expr {
	
	public static final Expr NULL_EXPR = NullExpr.me;
	public static final Expr[] NULL_EXPR_ARRAY = new Expr[0];
	public static final ExprList NULL_EXPR_LIST = new ExprList(new ArrayList(0));
	
	public static final Object[] NULL_OBJECT_ARRAY =  new Object[0];
	
	private Expr[] exprArray;
	
	public ExprList(List exprList) {
		if (exprList.size() > 0) {
			exprArray = exprList.toArray(new Expr[exprList.size()]);
		} else {
			exprArray = NULL_EXPR_ARRAY;
		}
	}
	
	/**
	 * 持有 ExprList 的指令可以通过此方法提升 AST 执行性能
	 * 1：当 exprArray.length == 1 时返回 exprArray[0]
	 * 2：当 exprArray.length == 0 时返回 NullExpr
	 * 3：其它情况返回 ExprList 自身
	 * 
	 * 意义在于，当满足前面两个条件时，避免掉了 ExprList.eval(...) 方法中的判断与循环
	 */
	public Expr getActualExpr() {
		if (exprArray.length == 1) {
			return exprArray[0];
		} else if (exprArray.length == 0) {
			return NULL_EXPR;
		} else {
			return this;
		}
	}
	
	public Expr[] getExprArray() {
		return exprArray;
	}
	
	public Expr getExpr(int index) {
		if (index < 0 || index >= exprArray.length) {
			throw new TemplateException("Index out of bounds: index = " + index + ", length = " + exprArray.length, location);
		}
		return exprArray[index];
	}
	
	public Expr getFirstExpr() {
		return exprArray.length > 0 ? exprArray[0] : null;
	}
	
	public Expr getLastExpr() {
		return exprArray.length > 0 ? exprArray[exprArray.length - 1] : null;
	}
	
	public int length() {
		return exprArray.length;
	}
	
	/**
	 * 对所有表达式求值，只返回最后一个表达式的值
	 */
	public Object eval(Scope scope) {
		// 优化：绝大多数情况下 length 等于 1
		if (exprArray.length == 1) {
			return exprArray[0].eval(scope);
		}
		
		if (exprArray.length == 0) {
			return null;
		}
		
		int end = exprArray.length - 1;
		for (int i=0; i