String builder optimization (ARCH608)

Key dotnet.performance.string-builder-optimization · Severity info · Category performance

Providing an approximate initial capacity prevents StringBuilder from repeatedly growing and reallocating its internal buffer.

Incorrect

var sb = new StringBuilder();
foreach (var line in lines) // thousands of lines
    sb.AppendLine(line);

Correct

var sb = new StringBuilder(lines.Count * 64);
foreach (var line in lines)
    sb.AppendLine(line);

Fix

Construct StringBuilder with an initial capacity when the expected size is known.