use a StringBuilder when converting to string

Author: WalkerCodeRanger

Semver.Test/IntExtensionsTests.cs

@@ -0,0 +1,26 @@
+using System.Globalization;
+using Xunit;
+
+namespace Semver.Test
+{
+    public class IntExtensionsTests
+    {
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1)]
+        [InlineData(9)]
+        [InlineData(10)]
+        [InlineData(986)]
+        [InlineData(4569)]
+        [InlineData(96854)]
+        [InlineData(565627)]
+        [InlineData(6615776)]
+        [InlineData(78415675)]
+        [InlineData(787_415_757)]
+        [InlineData(int.MaxValue)]
+        public void DigitsTest(int n)
+        {
+            Assert.Equal(n.ToString(CultureInfo.InvariantCulture).Length, n.Digits());
+        }
+    }
+}

Semver/IntExtensions.cs

@@ -0,0 +1,33 @@
+using System.Text;
+
+namespace Semver
+{
+    internal static class IntExtensions
+    {
+        /// <summary>
+        /// The number of digits in a non-negative number. Returns 1 for all
+        /// negative numbers. That is ok because we are using it to calculate
+        /// string length for a <see cref="StringBuilder"/> for numbers that
+        /// aren't supposed to be negative, but when they are it is just a little
+        /// slower.
+        /// </summary>
+        /// <remarks>
+        /// This approach is based on https://stackoverflow.com/a/51099524/268898
+        /// where the poster offers performance benchmarks showing this is the
+        /// fastest way to get a number of digits.
+        /// </remarks>
+        public static int Digits(this int n)
+        {
+            if (n < 10) return 1;
+            if (n < 100) return 2;
+            if (n < 1000) return 3;
+            if (n < 10000) return 4;
+            if (n < 100000) return 5;
+            if (n < 1000000) return 6;
+            if (n < 10000000) return 7;
+            if (n < 100000000) return 8;
+            if (n < 1000000000) return 9;
+            return 10;
+        }
+    }
+}

Semver/Properties/AssemblyInfo.cs

@@ -1,4 +1,7 @@
-using System.Runtime.InteropServices;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 [assembly: ComVisible(false)]
-[assembly: Guid("e208ca67-5b59-45d9-a29a-7f30137d3beb")]
+[assembly: Guid("e208ca67-5b59-45d9-a29a-7f30137d3beb")]
+
+[assembly: InternalsVisibleTo("Semver.Test")]

Semver/SemVersion.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Globalization;
+using System.Text;
 #if !NETSTANDARD
 using System.Runtime.Serialization;
 using System.Security.Permissions;
@@ -279,12 +280,26 @@ public SemVersion Change(int? major = null, int? minor = null, int? patch = null
         /// </returns>
         public override string ToString()
         {
-            var version = "" + Major + "." + Minor + "." + Patch;
-            if (!string.IsNullOrEmpty(Prerelease))
-                version += "-" + Prerelease;
-            if (!string.IsNullOrEmpty(Build))
-                version += "+" + Build;
-            return version;
+            // Assume all separators ("..-+"), at most 2 extra chars
+            var estimatedLength = 4 + Major.Digits() + Minor.Digits() + Patch.Digits()
+                                  + Prerelease.Length + Build.Length;
+            var version = new StringBuilder(estimatedLength);
+            version.Append(Major);
+            version.Append('.');
+            version.Append(Minor);
+            version.Append('.');
+            version.Append(Patch);
+            if (Prerelease.Length > 0)
+            {
+                version.Append('-');
+                version.Append(Prerelease);
+            }
+            if (Build.Length > 0)
+            {
+                version.Append('+');
+                version.Append(Build);
+            }
+            return version.ToString();
         }
 
         /// <summary>