Add player input routines

53_King/csharp/ValidityTest.cs

@@ -0,0 +1,26 @@
+namespace King;
+
+internal class ValidityTest
+{
+    private readonly Predicate<float> _isValid;
+    private readonly Func<string> _getError;
+
+    public ValidityTest(Predicate<float> isValid, string error)
+        : this(isValid, () => error)
+    {
+    }
+
+    public ValidityTest(Predicate<float> isValid, Func<string> getError)
+    {
+        _isValid = isValid;
+        _getError = getError;
+    }
+
+    public bool IsValid(float value, IReadWrite io)
+    {
+        if (_isValid(value)) { return true; }
+        
+        io.Write(_getError());
+        return false;
+    }
+}