hunt.sql.visitor.functions.Greatest source code

1 /*
2  * Copyright 2015-2018 HuntLabs.cn
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 module hunt.sql.visitor.functions.Greatest;
17 
18 // import hunt.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
19 
20 import hunt.sql.ast.SQLExpr;
21 import hunt.sql.ast.expr.SQLMethodInvokeExpr;
22 import hunt.sql.visitor.SQLEvalVisitor;
23 import hunt.sql.visitor.SQLEvalVisitorUtils;
24 import hunt.sql.visitor.functions.Function;
25 
26 import std.concurrency : initOnce;
27 
28 public class Greatest : Function {
29     
30     static Greatest instance() {
31         __gshared Greatest inst;
32         return initOnce!inst(new Greatest());
33     }    
34 
35     // public  static Greatest instance;
36 
37     // static this()
38     // {
39     //     instance = new Greatest();
40     // }
41 
42     public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
43         Object result = null;
44         foreach(SQLExpr item ; x.getParameters()) {
45             item.accept(visitor);
46 
47             Object itemValue = item.getAttributes().get(SQLEvalVisitor.EVAL_VALUE);
48             if (result is null) {
49                 result = itemValue;
50             } else {
51                 if (SQLEvalVisitorUtils.gt(itemValue, result)) {
52                     result = itemValue;
53                 }
54             }
55         }
56 
57         return result;
58     }
59 }