Specifying the message that the value not satisfy the restriction

Core/NetArgumentParser/Options/Configuration/OptionValueRestriction.cs

@@ -2,4 +2,4 @@
 
 namespace NetArgumentParser.Options.Configuration;
 
-public record OptionValueRestriction<T>(Predicate<T> IsValueAllowed);
+public record OptionValueRestriction<T>(Predicate<T> IsValueAllowed, string? ValueNotSatisfyRestrictionMessage = null);

Core/NetArgumentParser/Options/ValueOption.cs

@@ -94,12 +94,17 @@ protected ValueOption(
         if (valueRestriction is not null)
         {
             if (defaultValue is not null && !valueRestriction.IsValueAllowed(defaultValue.Value))
-                throw new OptionValueNotSatisfyRestrictionException(null, [$"{defaultValue.Value}"]);
+            {
+                throw new OptionValueNotSatisfyRestrictionException(
+                    valueRestriction.ValueNotSatisfyRestrictionMessage,
+                    [$"{defaultValue.Value}"]);
+            }
 
             if (_choices.Count > 0 && _choices.Any(t => !valueRestriction.IsValueAllowed(t)))
             {
                 throw new OptionValueNotSatisfyRestrictionException(
-                    null, [$"{_choices.First(t => !valueRestriction.IsValueAllowed(t))}"]);
+                    valueRestriction.ValueNotSatisfyRestrictionMessage,
+                    [$"{_choices.First(t => !valueRestriction.IsValueAllowed(t))}"]);
             }
         }
 
@@ -384,7 +389,11 @@ protected void VerifyValueIsAllowed(T value, string[] valueSource)
         ExtendedArgumentNullException.ThrowIfNull(valueSource, nameof(valueSource));
 
         if (!IsValueSatisfyRestriction(value))
-            throw new OptionValueNotSatisfyRestrictionException(null, valueSource);
+        {
+            throw new OptionValueNotSatisfyRestrictionException(
+                ValueRestriction?.ValueNotSatisfyRestrictionMessage,
+                valueSource);
+        }
 
         if (!IsValueSatisfyChoices(value))
         {

Documentation/OptionalArgumentsConfig.md

@@ -200,6 +200,16 @@ var enumValueOption = new EnumValueOption<StringSplitOptions>("options", "o",
     valueRestriction: new OptionValueRestriction<StringSplitOptions>(t => t != StringSplitOptions.None));
 ```
 
+You can also specify a message to be shown if the value doesn't satisfy the restriction:
+
+```cs
+var restriction = new OptionValueRestriction<int>(t => t > 0, "angle must be greater than zero");
+
+var valueOption = new ValueOption<int>("angle", "a",
+    description: "angle by which you want to rotate the image",
+    valueRestriction: restriction);
+```
+
 ### Required Options
 You can indicate that the option is required. In this case, if the input argument list doesn't contain a matching argument, an exception will be thrown.
 

Examples/NetArgumentParser.Examples.AllUseCases/Program.cs

@@ -85,7 +85,9 @@
         shortName: "i",
         description: "images that need to be processed",
         isRequired: true,
-        valueRestriction: new OptionValueRestriction<IList<string>>(t => t.All(p => File.Exists(p))),
+        valueRestriction: new OptionValueRestriction<IList<string>>(
+            t => t.All(p => File.Exists(p)),
+            "all files must exist"),
         contextCapture: new OneOrMoreContextCapture(),
         afterValueParsingAction: t => resultValues.InputFiles = [.. t]),
 

Examples/NetArgumentParser.Examples.OptionalArguments/Program.cs

@@ -70,7 +70,9 @@
         shortName: "i",
         description: "images that need to be processed",
         isRequired: true,
-        valueRestriction: new OptionValueRestriction<IList<string>>(t => t.All(p => File.Exists(p))),
+        valueRestriction: new OptionValueRestriction<IList<string>>(
+            t => t.All(p => File.Exists(p)),
+            "all files must exist"),
         contextCapture: new OneOrMoreContextCapture(),
         afterValueParsingAction: t => resultValues.InputFiles = [.. t]),