hunt.sql.visitor.functions.Reverse 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.Reverse;
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.functions.Function;
24 //import hunt.lang;
25 import hunt.String;
26 import hunt.String;
27 import hunt.collection;
28 import std.conv;
29 import std.uni;
30 import hunt.text;
31 
32 import std.concurrency : initOnce;
33 
34 public class Reverse : Function {
35 
36     static Reverse instance() {
37         __gshared Reverse inst;
38         return initOnce!inst(new Reverse());
39     } 
40         
41     // public  static Reverse instance;
42 
43     // static this()
44     // {
45     //     instance = new Reverse();
46     // }
47     
48     public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
49         if (x.getParameters().size() != 1) {
50             return cast(Object)(SQLEvalVisitor.EVAL_ERROR);
51         }
52 
53         SQLExpr param0 = x.getParameters().get(0);
54         param0.accept(visitor);
55 
56         Object param0Value = param0.getAttributes().get(SQLEvalVisitor.EVAL_VALUE);
57         if (param0Value is null) {
58             return cast(Object)(SQLEvalVisitor.EVAL_ERROR);
59         }
60 
61         string strValue = param0Value.toString();
62 
63         StringBuilder buf = new StringBuilder();
64         for (int i = cast(int)(strValue.length) - 1; i >= 0; --i) {
65             buf.append(charAt(strValue, i));
66         }
67         string result = buf.toString();
68         return new String(result);
69     }
70 }