Hide validator behind validator interface

src/Lemonad.ErrorHandling/IValidator.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using Lemonad.ErrorHandling.Internal;
+
+namespace Lemonad.ErrorHandling {
+    /// <summary>
+    /// An <typeparamref name="TError"/> collection of <typeparamref name="TError"/> based on validations of <typeparamref name="T"/>.
+    /// </summary>
+    /// <typeparam name="T">
+    /// The type of the validation candidate.
+    /// </typeparam>
+    /// <typeparam name="TError">
+    /// The type of the the error type.
+    /// </typeparam>
+    public interface IValidator<out T, TError> : IReadOnlyCollection<TError> {
+        /// <summary>
+        /// Validate <typeparamref name="T"/> with an <paramref name="predicate"/> function and set the failure type in <paramref name="errorSelector"/>.
+        /// </summary>
+        /// <param name="predicate">
+        /// A function to test <typeparamref name="T"/> for a condition.
+        /// </param>
+        /// <param name="errorSelector">
+        /// A function to set the error if the predicate function would return false.
+        /// </param>
+        /// <returns>
+        /// An <see cref="Validator{T,TError}"/>.
+        /// </returns>
+        IValidator<T, TError> Validate(Func<T, bool> predicate, Func<T, TError> errorSelector);
+
+        /// <summary>
+        /// Validate <typeparamref name="T"/> with an <paramref name="predicate"/> function and set the failure type with <paramref name="error"/>.
+        /// </summary>
+        /// <param name="predicate">
+        /// A function to test <typeparamref name="T"/> for a condition.
+        /// </param>
+        /// <param name="error">
+        /// The error value.
+        /// </param>
+        /// <returns>
+        /// An <see cref="Validator{T,TError}"/>.
+        /// </returns>
+        IValidator<T, TError> Validate(Func<T, bool> predicate, TError error);
+
+        /// <summary>
+        /// Gets the <see cref="IResult{T,TError}"/>.
+        /// </summary>
+        IResult<T, IReadOnlyCollection<TError>> Result { get; }
+    }
+}

src/Lemonad.ErrorHandling/Internal/Validator.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Lemonad.ErrorHandling.Internal {
+    internal readonly struct Validator<T, TError> : IValidator<T, TError> {
+        private readonly T _candidate;
+        private readonly Queue<TError> _errors;
+
+        public IResult<T, IReadOnlyCollection<TError>> Result { get; }
+
+        internal Validator(T candidate) {
+            _candidate = candidate;
+            _errors = new Queue<TError>();
+            Result = ErrorHandling.Result.Value<T, IReadOnlyCollection<TError>>(_candidate);
+        }
+
+        private Validator(in Queue<TError> errors, in T candidate) {
+            _errors = new Queue<TError>(errors);
+            _candidate = candidate;
+            Result = _errors.Count > 0
+                ? ErrorHandling.Result.Error<T, IReadOnlyCollection<TError>>(_errors)
+                : ErrorHandling.Result.Value<T, IReadOnlyCollection<TError>>(_candidate);
+        }
+
+        public IEnumerator<TError> GetEnumerator() => _errors.GetEnumerator();
+
+        public IValidator<T, TError> Validate(Func<T, bool> predicate, Func<T, TError> errorSelector) {
+            if (predicate == null) throw new ArgumentException(nameof(predicate));
+            if (errorSelector == null) throw new ArgumentException(nameof(errorSelector));
+            var result = _candidate.ToResult(predicate, errorSelector);
+            // This refers to the initial queue.
+            if (result.Either.HasError) _errors.Enqueue(result.Either.Error);
+            return new Validator<T, TError>(_errors, _candidate);
+        }
+
+        public IValidator<T, TError> Validate(Func<T, bool> predicate, TError error) => Validate(predicate, _ => error);
+
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+        public int Count => _errors.Count;
+    }
+}

src/Lemonad.ErrorHandling/Validator.cs

@@ -1,87 +1,20 @@
-using System;
-using System.Collections;
-using System.Collections.Generic;
+using System;
 using Lemonad.ErrorHandling.Internal;
 
 namespace Lemonad.ErrorHandling {
-    /// <summary>
-    /// An <typeparamref name="TError"/> collection of <typeparamref name="TError"/> based on validations of <typeparamref name="T"/>.
-    /// </summary>
-    /// <typeparam name="T">
-    /// The type of the validation candidate.
-    /// </typeparam>
-    /// <typeparam name="TError">
-    /// The type of the the error type.
-    /// </typeparam>
-    public readonly struct Validator<T, TError> : IReadOnlyCollection<TError> {
-        private readonly T _candidate;
-        private readonly Queue<TError> _errors;
-
-        /// <summary>
-        /// Convert to a <see cref="Result{T,TError}"/>.
-        /// </summary>
-        public IResult<T, IReadOnlyCollection<TError>> Result {
-            get {
-                var candidate = _candidate;
-                return _errors.ToResultError<T, IReadOnlyCollection<TError>>(x => x.Count > 0, _ => candidate);
-            }
-        }
-
-        /// <summary>
-        ///  Creates an instance of <see cref="Validator{T,TError}"/>.
-        /// </summary>
-        /// <param name="candidate">
-        /// The validation <paramref name="candidate"/>.
-        /// </param>
-        public Validator(T candidate) {
-            _candidate = candidate;
-            _errors = new Queue<TError>();
-        }
-
-        private Validator(in Queue<TError> errors, in T candidate) {
-            _errors = errors;
-            _candidate = candidate;
-        }
-
-        /// <inheritdoc cref="IEnumerable{T}.GetEnumerator"/>
-        public IEnumerator<TError> GetEnumerator() => _errors.GetEnumerator();
-
-        /// <summary>
-        /// Validate <typeparamref name="T"/> with an <paramref name="predicate"/> function and set the failure type in <paramref name="errorSelector"/>.
-        /// </summary>
-        /// <param name="predicate">
-        /// A function to test <typeparamref name="T"/> for a condition.
-        /// </param>
-        /// <param name="errorSelector">
-        /// A function to set the error if the predicate function would return false.
-        /// </param>
-        /// <returns>
-        /// An <see cref="Validator{T,TError}"/>.
-        /// </returns>
-        public Validator<T, TError> Validate(Func<T, bool> predicate, Func<TError> errorSelector) {
-            var result = _candidate.ToResult(predicate, _ => errorSelector());
-            if (result.Either.HasError) _errors.Enqueue(result.Either.Error);
-            return new Validator<T, TError>(_errors, _candidate);
-        }
-
-        /// <summary>
-        /// Validate <typeparamref name="T"/> with an <paramref name="predicate"/> function and set the failure type with <paramref name="error"/>.
-        /// </summary>
-        /// <param name="predicate">
-        /// A function to test <typeparamref name="T"/> for a condition.
-        /// </param>
-        /// <param name="error">
-        /// The error value.
-        /// </param>
-        /// <returns>
-        /// An <see cref="Validator{T,TError}"/>.
-        /// </returns>
-        public Validator<T, TError> Validate(Func<T, bool> predicate, TError error) => Validate(predicate, () => error);
-
-        /// <inheritdoc cref="IEnumerable.GetEnumerator"/>
-        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
-
-        /// <inheritdoc cref="IReadOnlyCollection{T}.Count"/>
-        public int Count => _errors.Count;
+    public static class Validator {
+        public static IValidator<T, TError> Value<T, TError>(T value) => new Validator<T, TError>(value);
+
+        public static IValidator<T, TError> Value<T, TError>(
+            T value,
+            Func<T, bool> predicate,
+            Func<T, TError> errorSelector
+        ) => new Validator<T, TError>(value).Validate(predicate, errorSelector);
+
+        public static IValidator<T, TError> Value<T, TError>(
+            T value,
+            Func<T, bool> predicate,
+            TError errorSelector
+        ) => new Validator<T, TError>(value).Validate(predicate, errorSelector);
     }
 }

test/Lemonad.ErrorHandling.Test/Validator.Tests/ValidateTests.cs

@@ -6,50 +6,124 @@ public class ValidateTests {
         [Fact]
         public void Single_False_Validation() {
             const string error = "Not dividable by 2";
-            var validator = new Validator<int, string>(1).Validate(i => i % 2 == 0, error).ToList();
+            var validator = ErrorHandling.Validator.Value<int, string>(1).Validate(i => i % 2 == 0, error).ToList();
             Assert.Single(validator, error);
         }
 
         [Fact]
         public void Single_True_Validation() {
             const string error = "Not dividable by 2";
-            var validator = new Validator<int, string>(2).Validate(i => i % 2 == 0, error).ToList();
+            var validator = ErrorHandling.Validator.Value<int, string>(2).Validate(i => i % 2 == 0, error).ToList();
             Assert.Empty(validator);
         }
 
         [Fact]
         public void Double_True_Validation() {
             const string error1 = "Not dividable by 2";
             const string error2 = "Is equal to 2.";
-            var validator = new Validator<int, string>(2)
+            var validator = ErrorHandling.Validator.Value<int, string>(2)
                 .Validate(i => i % 2 == 0, error1)
-                .Validate(i => i == 2, () => error2)
+                .Validate(i => i == 2, x => error2)
                 .ToList();
             Assert.Empty(validator);
         }
 
+        [Fact]
+        public void Double_True_Validation_Verify_States() {
+            const string error1 = "Not dividable by 2";
+            const string error2 = "Is equal to 2.";
+            var state0 = ErrorHandling.Validator.Value<int, string>(2);
+            Assert.Empty(state0);
+            var state1 = state0.Validate(i => i % 2 == 0, error1);
+            Assert.Empty(state1);
+            var state2 = state1.Validate(i => i == 2, x => error2);
+            Assert.Empty(state2);
+            var validator = state2.ToList();
+            Assert.Empty(validator);
+        }
+
         [Fact]
         public void Double_False_Validation() {
             const string error1 = "Is not equal to 0";
             const string error2 = "Not dividable by 2";
-            var validator = new Validator<int, string>(1)
-                .Validate(i => i == 0, () => error1)
-                .Validate(i => i % 2 == 0, () => error2)
+            var validator = ErrorHandling.Validator.Value<int, string>(1)
+                .Validate(i => i == 0, x => error1)
+                .Validate(i => i % 2 == 0, x => error2)
                 .ToList();
             Assert.Equal(2, validator.Count);
             Assert.Equal(error1, validator[0]);
             Assert.Equal(error2, validator[1]);
         }
 
         [Fact]
-        public void Single_True_Validation_And_Single_False_Validation() {
+        public void Double_False_Validation_Verify_States() {
+            const string error1 = "Is not equal to 0";
+            const string error2 = "Not dividable by 2";
+            var state0 = ErrorHandling.Validator.Value<int, string>(1);
+            Assert.Empty(state0);
+            var state1 = state0.Validate(i => i == 0, x => error1);
+            Assert.Single(state1);
+            var state2 = state1.Validate(i => i % 2 == 0, x => error2);
+            Assert.Equal(2, state2.Count);
+            var validator = state2.ToList();
+            Assert.Equal(2, validator.Count);
+            Assert.Equal(error1, validator[0]);
+            Assert.Equal(error2, validator[1]);
+        }
+
+        [Fact]
+        public void First_False_Validation_And_Second_True_Validation_Verify_States() {
+            const string error1 = "Is not equal to 0";
+            const string error2 = "Not dividable by 2";
+            var state0 = ErrorHandling.Validator.Value<int, string>(2);
+            var state1 = state0.Validate(i => i == 0, x => error1);
+            var state2 = state1.Validate(i => i % 2 == 0, x => error2);
+            // These errors occur since the collection in `state2` references the collection in `state0`.
+            // So all errors in `state2` are found in `state0` therefor.
+            Assert.Empty(state0);
+            Assert.Single(state1);
+            Assert.Single(state2);
+        }
+
+        [Fact]
+        public void First_True_Validation_And_Second_False_Validation_Verify_States() {
             const string error1 = "Is not equal to 0";
             const string error2 = "Not dividable by 2";
-            var validator = new Validator<int, string>(2)
-                .Validate(i => i == 0, () => error1)
-                .Validate(i => i % 2 == 0, () => error2)
+            var state0 = ErrorHandling.Validator.Value<int, string>(2);
+            var state1 = state0.Validate(i => i % 2 == 0, x => error2);
+            var state2 = state1.Validate(i => i == 0, x => error1);
+            Assert.Empty(state0);
+            Assert.Empty(state1);
+            Assert.Single(state2);
+        }
+
+        [Fact]
+        public void First_False_Validation_And_Second_True_Validation() {
+            const string error1 = "Is not equal to 0";
+            const string error2 = "Not dividable by 2";
+            var validator = ErrorHandling.Validator.Value<int, string>(2)
+                .Validate(i => i == 0, x => error1)
+                .Validate(i => i % 2 == 0, x => error2)
                 .ToList();
             Assert.Single(validator);
         }
+
+        [Fact]
+        public void First_True_Validation_And_Second_False_Validation() {
+            const string error1 = "Is not equal to 0";
+            const string error2 = "Not dividable by 2";
+            var validator = ErrorHandling.Validator.Value<int, string>(2)
+                .Validate(i => i % 2 == 0, x => error2)
+                .Validate(i => i == 0, x => error1)
+                .ToList();
+            Assert.Single(validator);
+        }
+
+        [Fact]
+        public void Result_Does_Not_Create_New_Instance_On_Get() {
+            var validator = ErrorHandling.Validator.Value<int, string>(2);
+            Assert.Equal(validator.Result, validator.Result);
+            Assert.StrictEqual(validator.Result, validator.Result);
+        }
     }
 }