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POC# & T-SQL string[] Pack/Unpack utility functions
 

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  1. POC# & T-SQL string[] Pack/Unpack utility functions
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    <p>Can anyone skilled in t-sql create companion table-valued functions to these C# array pack &amp; unpack utility methods that escape delimiters and preserve nulls, null arrays, empty arrays through roundtrip encoding?</p> <p>By packing any variety of string arrays into a string, you can pass such (small) arrays to SQL as parameters, which is useful in some scenarios.</p> <pre><code>static class ArrayUtil { public static string Pack(string[] original) { return Pack(original, '|', '0', '~'); } public static string[] Unpack(string original) { return Unpack(original, '|', '0', '~'); } public static string Pack(string[] original, char delimiter, char zed, char escape) { if (delimiter == escape || zed == escape || delimiter == zed) throw new ArgumentException("special characters must be distinct"); // Null array returns a null string if (original == null) return null; // Empty array returns an empty string if (original.Length == 0) return string.Empty; // Arrays with a single empty element are represented as just the escape character // to differentiate from an empty array if (original.Length == 1 &amp;&amp; original[0] == string.Empty) return escape.ToString(); // Otherwise StringBuilder sb = new StringBuilder(); for (int i = 0, ol = original.Length; i &lt; ol; i++) { string s = original[i]; if (s == null) { sb.Append(zed); // zed == null } else { for (int j = 0, sl = s.Length; j &lt; sl; j++) { char c = s[j]; // escape literal delimiters, escapes, and leading zeds if (c == delimiter || c == escape || (c == zed &amp;&amp; j == 0)) sb.Append(escape); sb.Append(c); } } if (i != ol - 1) sb.Append(delimiter); // no trailing delimiter } return sb.ToString(); } public static string[] Unpack(string original, char delimiter, char zed, char escape) { if (delimiter == escape || zed == escape || delimiter == zed) throw new ArgumentException("special characters must be distinct"); // Null string returns a null array if (original == null) return null; // Empty string returns an empty array if (original == string.Empty) return new string[] { }; // A single escape character represents an array with a single empty element // to differentiate from an empty array if (original == escape.ToString()) return new string[] { string.Empty }; // Otherwise StringBuilder sb = new StringBuilder(); // A place to store the current element StringReader sr = new StringReader(original); // A stream of the original string List&lt;string&gt; unpacked = new List&lt;string&gt;(); // The finished elements int next; while ((next = sr.Read()) &gt;= 0) { char c = (char)next; if (c == zed &amp;&amp; sb.Length == 0) { unpacked.Add(null); if ((next = sr.Peek()) &gt;= 0 &amp;&amp; (char)next != delimiter) throw new ArgumentException("An element's leading zed character must be escaped or must alone be the element", "original"); sb = null; } else if (c == delimiter) { if (sb != null) unpacked.Add(sb.ToString()); sb = new StringBuilder(); } else if (c == escape) { if ((next = sr.Read()) &gt;= 0) { sb.Append((char)next); } else throw new ArgumentException("Escapee expected", "original"); } else { sb.Append(c); } } // A final zed character will make sb = null, but otherwise we have an additional element if (sb != null) unpacked.Add(sb.ToString()); return unpacked.ToArray(); } } </code></pre> <p>Example packings with <code>Pack(original, '|', '0', '~')</code>, basic case:</p> <pre><code>["hello", "world"] -&gt; "hello|world" </code></pre> <p>Some special cases (as discovered by PEX)</p> <pre><code>null -&gt; null [null] -&gt; "0" [null, null] -&gt; "0|0" [] -&gt; "" [""] -&gt; "~" ["", ""] -&gt; "|" ["|", "|"] -&gt; "~||~|" </code></pre>
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