Replaces the single-iteration foreach loops (#48)

* Replaces the single-iteration foreach loops with direct calls to GetEnumerator.MoveNext().

* Adds unit tests for That and ValidState.

* Wrapping the enumerator in a try..finally to ensure it's disposed of it also implements IDisposable.

* Update Requires.cs

src/Validation/Requires.cs

@@ -4,6 +4,7 @@
 namespace Validation
 {
     using System;
+    using System.Collections;
     using System.Collections.Generic;
     using System.ComponentModel;
     using System.Diagnostics;
@@ -179,7 +180,7 @@ public static void NotNullOrWhiteSpace([ValidatedNotNull, NotNull] string value,
         /// <param name="parameterName">The name of the parameter to include in any thrown exception.</param>
         /// <exception cref="ArgumentException">Thrown if the tested condition is false.</exception>
         [DebuggerStepThrough]
-        public static void NotNullOrEmpty([ValidatedNotNull, NotNull] System.Collections.IEnumerable values, string? parameterName)
+        public static void NotNullOrEmpty([ValidatedNotNull, NotNull] IEnumerable values, string? parameterName)
         {
             // To whoever is doing random code cleaning:
             // Consider the performance when changing the code to delegate to NotNull.
@@ -189,16 +190,13 @@ public static void NotNullOrEmpty([ValidatedNotNull, NotNull] System.Collections
                 throw new ArgumentNullException(parameterName);
             }
 
-            bool hasElements = false;
-            foreach (object value in values)
-            {
-                hasElements = true;
-                break;
-            }
-
-            if (!hasElements)
+            IEnumerator enumerator = values.GetEnumerator();
+            using (enumerator as IDisposable)
             {
-                throw new ArgumentException(Format(Strings.Argument_EmptyArray, parameterName), parameterName);
+                if (!enumerator.MoveNext())
+                {
+                    throw new ArgumentException(Format(Strings.Argument_EmptyArray, parameterName), parameterName);
+                }
             }
         }
 
@@ -221,14 +219,8 @@ public static void NotNullOrEmpty<T>([ValidatedNotNull, NotNull] IEnumerable<T>
                 throw new ArgumentNullException(parameterName);
             }
 
-            bool hasElements = false;
-            foreach (T value in values)
-            {
-                hasElements = true;
-                break;
-            }
-
-            if (!hasElements)
+            using IEnumerator<T> enumerator = values.GetEnumerator();
+            if (!enumerator.MoveNext())
             {
                 throw new ArgumentException(Format(Strings.Argument_EmptyArray, parameterName), parameterName);
             }

test/Validation.Tests/RequiresTests.cs

@@ -248,4 +248,19 @@ public void ValidElements()
         Requires.ValidElements(new[] { "a", "b", "c", "d" }, x => !string.IsNullOrWhiteSpace(x), "param", "test message: {0}", "param");
         Requires.ValidElements(new[] { 1, 2 }, v => v > 0, "param", "{0} must be greater than 0.", "param");
     }
+
+    [Fact]
+    public void That()
+    {
+        Requires.That(true, "param", "{0} must be true.", "param");
+        Assert.Contains("param must be true", Assert.Throws<ArgumentException>(() => Requires.That(false, "param", "{0} must be true.", "param")).Message, StringComparison.InvariantCultureIgnoreCase);
+        Assert.Contains("param must be true", Assert.Throws<ArgumentException>(() => Requires.That(false, null, "{0} must be true.", "param")).Message, StringComparison.InvariantCultureIgnoreCase);
+    }
+
+    [Fact]
+    public void ValidState()
+    {
+        Requires.ValidState(true, "Condition must be true.");
+        Assert.Contains("Condition must be true", Assert.Throws<InvalidOperationException>(() => Requires.ValidState(false, "Condition must be true.")).Message, StringComparison.InvariantCultureIgnoreCase);
+    }
 }