mcs/class/referencesource/System.Data.SqlXml/System/Xml/Xsl/Runtime/StringConcat.cs

   1 //------------------------------------------------------------------------------
   2 // <copyright file="StringConcat.cs" company="Microsoft">
   3 //     Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 // <owner current="true" primary="true">Microsoft</owner>
   6 //------------------------------------------------------------------------------
   7 using System;
   8 using System.Collections.Generic;
   9 using System.Diagnostics;
  10 using System.ComponentModel;
  11
  12 namespace System.Xml.Xsl.Runtime {
  13
  14     /// <summary>
  15     /// Efficiently concatenates strings when the number of string is not known beforehand, and
  16     /// yet it is common for only one string to be concatenated.  StringBuilder is not good for
  17     /// this purpose, since it *always* allocates objects, even if only one string is appended.
  18     /// </summary>
  19     [EditorBrowsable(EditorBrowsableState.Never)]
  20     public struct StringConcat {
  21         private string s1, s2, s3, s4;
  22         private string delimiter;
  23         private List<string> strList;
  24         int idxStr;
  25
  26         /// <summary>
  27         /// Clear the result string.
  28         /// </summary>
  29         public void Clear() {
  30             this.idxStr = 0;
  31             this.delimiter = null;
  32         }
  33
  34         /// <summary>
  35         /// Gets or sets the string that delimits concatenated strings.
  36         /// </summary>
  37         public string Delimiter {
  38             get { return this.delimiter; }
  39             set { this.delimiter = value; }
  40         }
  41
  42         /// <summary>
  43         /// Return the number of concatenated strings, including delimiters.
  44         /// </summary>
  45         internal int Count {
  46             get { return this.idxStr; }
  47         }
  48
  49         /// <summary>
  50         /// Concatenate a new string to the result.
  51         /// </summary>
  52         public void Concat(string value) {
  53             Debug.Assert(value != null);
  54
  55             if (this.delimiter != null && this.idxStr != 0) {
  56                 // Add delimiter
  57                 ConcatNoDelimiter(this.delimiter);
  58             }
  59
  60             ConcatNoDelimiter(value);
  61         }
  62
  63         /// <summary>
  64         /// Get the result string.
  65         /// </summary>
  66         public string GetResult() {
  67             switch (this.idxStr) {
  68                 case 0: return string.Empty;
  69                 case 1: return this.s1;
  70                 case 2: return string.Concat(this.s1, this.s2);
  71                 case 3: return string.Concat(this.s1, this.s2, this.s3);
  72                 case 4: return string.Concat(this.s1, this.s2, this.s3, this.s4);
  73             }
  74             return string.Concat(this.strList.ToArray());
  75         }
  76
  77         /// <summary>
  78         /// Concatenate a new string to the result without adding a delimiter.
  79         /// </summary>
  80         internal void ConcatNoDelimiter(string s) {
  81             switch (this.idxStr) {
  82                 case 0: this.s1 = s; break;
  83                 case 1: this.s2 = s; break;
  84                 case 2: this.s3 = s; break;
  85                 case 3: this.s4 = s; break;
  86                 case 4:
  87                     // Calling Clear() is expensive, allocate a new List instead
  88                     int capacity = (this.strList == null) ? 8 : this.strList.Count;
  89                     List<string> strList = this.strList = new List<string>(capacity);
  90                     strList.Add(this.s1);
  91                     strList.Add(this.s2);
  92                     strList.Add(this.s3);
  93                     strList.Add(this.s4);
  94                     goto default;
  95                 default:
  96                     this.strList.Add(s);
  97                     break;
  98             }
  99
 100             this.idxStr++;
 101         }
 102     }
 103 }