Develop Reference

Why there is no expression sequencing operator? [duplicate]

I'm using some functional stuff in C# and keep getting stuck on the fact that List.Add doesn't return the updated list.
In general, I'd like to call a function on an object and then return the updated object.
For example it would be great if C# had a comma operator:
((accum, data) => accum.Add(data), accum)
I could write my own "comma operator" like this:
static T comma(Action a, Func<T> result) {
a();
return result();
}
It looks like it would work but the call site would ugly. My first example would be something like:
((accum, data) => comma(accum.Add(data), ()=>accum))
Enough examples! What's the cleanest way to do this without another developer coming along later and wrinkling his or her nose at the code smell?

I know this as Fluent.
A Fluent example of a List.Add using Extension Methods
static List<T> MyAdd<T>(this List<T> list, T element)
{
list.Add(element);
return list;
}

I know that this thread is very old, but I want to append the following information for future users:
There isn't currently such an operator. During the C# 6 development cycle a semicolon operator was added, as:
int square = (int x = int.Parse(Console.ReadLine()); Console.WriteLine(x - 2); x * x);
which can be translated as follows:
int square = compiler_generated_Function();
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private int compiler_generated_Function()
{
int x = int.Parse(Console.ReadLine());
Console.WriteLine(x - 2);
return x * x;
}
However, this feature was dropped before the final C# release.

You can do almost exactly the first example naturally using code blocks in C# 3.0.
((accum, data) => { accum.Add(data); return accum; })

This is what Concat http://msdn.microsoft.com/en-us/library/vstudio/bb302894%28v=vs.100%29.aspx is for. Just wrap a single item in an array. Functional code should not mutate the original data. If performance is a concern, and this isn't good enough, then you'll no longer be using the functional paradigm.
((accum, data) => accum.Concat(new[]{data}))

Another technique, straight from functional programming, is as follows. Define an IO struct like this:
/// <summary>TODO</summary>
public struct IO<TSource> : IEquatable<IO<TSource>> {
/// <summary>Create a new instance of the class.</summary>
public IO(Func<TSource> functor) : this() { _functor = functor; }
/// <summary>Invokes the internal functor, returning the result.</summary>
public TSource Invoke() => (_functor | Default)();
/// <summary>Returns true exactly when the contained functor is not null.</summary>
public bool HasValue => _functor != null;
X<Func<TSource>> _functor { get; }
static Func<TSource> Default => null;
}
and make it a LINQ-able monad with these extension methods:
[SuppressMessage("Microsoft.Naming", "CA1724:TypeNamesShouldNotMatchNamespaces")]
public static class IO {
public static IO<TSource> ToIO<TSource>( this Func<TSource> source) {
source.ContractedNotNull(nameof(source));
return new IO<TSource>(source);
}
public static IO<TResult> Select<TSource,TResult>(this IO<TSource> #this,
Func<TSource,TResult> projector
) =>
#this.HasValue && projector!=null
? New(() => projector(#this.Invoke()))
: Null<TResult>();
public static IO<TResult> SelectMany<TSource,TResult>(this IO<TSource> #this,
Func<TSource,IO<TResult>> selector
) =>
#this.HasValue && selector!=null
? New(() => selector(#this.Invoke()).Invoke())
: Null<TResult>();
public static IO<TResult> SelectMany<TSource,T,TResult>(this IO<TSource> #this,
Func<TSource, IO<T>> selector,
Func<TSource,T,TResult> projector
) =>
#this.HasValue && selector!=null && projector!=null
? New(() => { var s = #this.Invoke(); return projector(s, selector(s).Invoke()); } )
: Null<TResult>();
public static IO<TResult> New<TResult> (Func<TResult> functor) => new IO<TResult>(functor);
private static IO<TResult> Null<TResult>() => new IO<TResult>(null);
}
and now you can use the LINQ comprehensive syntax thus:
using Xunit;
[Fact]
public static void IOTest() {
bool isExecuted1 = false;
bool isExecuted2 = false;
bool isExecuted3 = false;
bool isExecuted4 = false;
IO<int> one = new IO<int>( () => { isExecuted1 = true; return 1; });
IO<int> two = new IO<int>( () => { isExecuted2 = true; return 2; });
Func<int, IO<int>> addOne = x => { isExecuted3 = true; return (x + 1).ToIO(); };
Func<int, Func<int, IO<int>>> add = x => y => { isExecuted4 = true; return (x + y).ToIO(); };
var query1 = ( from x in one
from y in two
from z in addOne(y)
from _ in "abc".ToIO()
let addOne2 = add(x)
select addOne2(z)
);
Assert.False(isExecuted1); // Laziness.
Assert.False(isExecuted2); // Laziness.
Assert.False(isExecuted3); // Laziness.
Assert.False(isExecuted4); // Laziness.
int lhs = 1 + 2 + 1;
int rhs = query1.Invoke().Invoke();
Assert.Equal(lhs, rhs); // Execution.
Assert.True(isExecuted1);
Assert.True(isExecuted2);
Assert.True(isExecuted3);
Assert.True(isExecuted4);
}
When one desires an IO monad that composes but returns only void, define this struct and dependent methods:
public struct Unit : IEquatable<Unit>, IComparable<Unit> {
[CLSCompliant(false)]
public static Unit _ { get { return _this; } } static Unit _this = new Unit();
}
public static IO<Unit> ConsoleWrite(object arg) =>
ReturnIOUnit(() => Write(arg));
public static IO<Unit> ConsoleWriteLine(string value) =>
ReturnIOUnit(() => WriteLine(value));
public static IO<ConsoleKeyInfo> ConsoleReadKey() => new IO<ConsoleKeyInfo>(() => ReadKey());
which readily allow the writing of code fragments like this:
from pass in Enumerable.Range(0, int.MaxValue)
let counter = Readers.Counter(0)
select ( from state in gcdStartStates
where _predicate(pass, counter())
select state )
into enumerable
where ( from _ in Gcd.Run(enumerable.ToList()).ToIO()
from __ in ConsoleWrite(Prompt(mode))
from c in ConsoleReadKey()
from ___ in ConsoleWriteLine()
select c.KeyChar.ToUpper() == 'Q'
).Invoke()
select 0;
where the old C comma operator is readily recognized for what it is: a monadic compose operation.
The true merit of the comprehension syntax is apparent when one attempts to write that fragment in the flunt style:
( Enumerable.Range(0,int.MaxValue)
.Select(pass => new {pass, counter = Readers.Counter(0)})
.Select(_ => gcdStartStates.Where(state => _predicate(_.pass,_.counter()))
.Select(state => state)
)
).Where(enumerable =>
( (Gcd.Run(enumerable.ToList()) ).ToIO()
.SelectMany(_ => ConsoleWrite(Prompt(mode)),(_,__) => new {})
.SelectMany(_ => ConsoleReadKey(), (_, c) => new {c})
.SelectMany(_ => ConsoleWriteLine(), (_,__) => _.c.KeyChar.ToUpper() == 'Q')
).Invoke()
).Select(list => 0);

The extension method is arguably the best solution, but for completeness' sake, don't forget the obvious alternative: a wrapper class.
public class FList<T> : List<T>
{
public new FList<T> Add(T item)
{
base.Add(item);
return this;
}
public new FList<T> RemoveAt(int index)
{
base.RemoveAt(index);
return this;
}
// etc...
}
{
var list = new FList<string>();
list.Add("foo").Add("remove me").Add("bar").RemoveAt(1);
}

I thought it would be interesting to make a version of my wrapper class answer that doesn't require you write the wrapper methods.
public class FList<T> : List<T>
{
public FList<T> Do(string method, params object[] args)
{
var methodInfo = GetType().GetMethod(method);
if (methodInfo == null)
throw new InvalidOperationException("I have no " + method + " method.");
if (methodInfo.ReturnType != typeof(void))
throw new InvalidOperationException("I'm only meant for void methods.");
methodInfo.Invoke(this, args);
return this;
}
}
{
var list = new FList<string>();
list.Do("Add", "foo")
.Do("Add", "remove me")
.Do("Add", "bar")
.Do("RemoveAt", 1)
.Do("Insert", 1, "replacement");
foreach (var item in list)
Console.WriteLine(item);
}
Output:
foo
replacement
bar
EDIT
You can slim down the syntax by exploiting C# indexed properties.
Simply add this method:
public FList<T> this[string method, params object[] args]
{
get { return Do(method, args); }
}
And the call now looks like:
list = list["Add", "foo"]
["Add", "remove me"]
["Add", "bar"]
["RemoveAt", 1]
["Insert", 1, "replacement"];
With the linebreaks being optional, of course.
Just a bit of fun hacking the syntax.

Updating object Linq'd from collection doesn't update the object in collection

I have two simple classes. One is called UseCounter<T> and is a simple container for other objects while holding some information about its use (how many times it's been already used and if it can be reused once again).
Then there is Dispenser<T>, which holds a collection of UseConter<T> and is used to get the right element from the collection and then update its information.
The trouble I have is in the Dispenser's Get() method. It should return the object with the lowest combination of Count and TotalCount, and then call Increase() method in order to increase count.
However, when I run this code, Dispenser<T> always returns the same element. It's like the Linq'd element wasn't a reference to the object, but its copy, so the Increase() method increases only the local object's properties, but not the one in the collection.
I am at loss here, because I have never encountered such a behaviour.
Here comes the code:
UseCounter:
public class UseCounter<T>
{
public T Element { get; private set; }
public int TotalCount { get; private set; }
public int Count { get; private set; }
public bool Useful { get; set; }
public UseCounter(T element)
{
this.Element = element;
this.Count = 0;
this.TotalCount = 0;
this.Useful = true;
}
public void IncreaseCounter()
{
this.Count++;
this.TotalCount++;
}
public void DecreaseCounter()
{
if(this.Count == 0)
{
throw new ArgumentOutOfRangeException("Count cannot be lower than 0!");
}
this.Count--;
}
}
Dispenser:
private readonly object _elementLocker = new object();
private IEnumerable<UseCounter<T>> _elements;
public IEnumerable<T> Elements
{
get { return _elements.Select(e => e.Element); }
}
public int FinishedCount
{
get
{
lock (_elementLocker)
{
return _elements.Where(e => e.Useful == false).Count();
}
}
}
public int CurrentlyWorkingCount
{
get
{
lock (_elementLocker)
{
return _elements.Where(e => e.Count > 0).Count();
}
}
}
public Dispenser(IEnumerable<T> elements)
{
this._elements = elements
.Distinct()
.Select(e => new UseCounter<T>(e));
}
public T Get()
{
lock(_elementLocker)
{
var lCount = _elements
.Where(e => e.Useful == true)
.Select(e => e.Count).Min();
var lTCount = _elements
.Where(e => e.Useful == true)
.Where(e => e.Count == lCount)
.Select(e => e.TotalCount).Min();
var el = _elements
.Where(e => e.Useful == true)
.First(e => e.Count == lCount && e.TotalCount == lTCount);
el.IncreaseCounter();
return el.Element;
}
}
public void Report(T element, bool successful)
{
lock(_elementLocker)
{
var el = _elements
.First(e => e.Element == element);
el.DecreaseCounter();
if(el.Useful == true && successful == true)
{
el.Useful = false;
}
}
}

This is the problem:
this._elements = elements
.Distinct()
.Select(e => new UseCounter<T>(e));
This is lazy. Every time you iterate over _elements, it will go back to the original source data, find a distinct set, and then project that set onto a new sequence of UseCounter instances. Any changes you make to those instances are irrelevant to what happens when you next iterate over _elements.
If you're happy for the set of input elements to be "frozen" on construction, you can just materialize the query so it only executes once:
this._elements = elements
.Distinct()
.Select(e => new UseCounter<T>(e))
.ToList();
Now every time you iterate over elements, you're iterating over the same sequence of references.

EF6 Mocking derived DbSets

I am trying to apply the new mocking of EF6 to my existing code.
I have a class that Extends DbSet. One of the methods call the base class (BdSet) Create method. Here is the a sample code (not the complete solution or real names):
public class DerivedDbSet<TEntity> : DbSet<TEntity>, IKeyValueDbSet<TEntity>, IOrderedQueryable<TEntity> where TEntity : class
{
public virtual bool Add(string value1, string value2) {
var entity = Create(); // There is no direct implementation of the Create method it is calling the base method
// Do something with the values
this.Add(entity);
return true;
}
}
I am mocking using the Test Doubles sample (here is the peace of code):
var data = new List<DummyEntity> {
new DummyEntity { Value1 = "First", Value2 = "001" },
new DummyEntity { Value1 = "Second", Value2 = "002" }
}.AsQueryable();
var mock = new Mock<DerivedDbSet<DummyEntity>>();
mock.CallBase = true;
mock.As<IQueryable<T>>().Setup(m => m.Provider).Returns(source.Provider);
mock.As<IQueryable<T>>().Setup(m => m.Expression).Returns(source.Expression);
mock.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(source.ElementType);
mock.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(source.GetEnumerator());
I've set the CallBase property to true to try to force the call to the base class...
But I keep receiving the following error:
System.NotImplementedException: The member 'Create' has not been implemented on type 'DerivedDbSet1Proxy' which inherits from 'DbSet1'. Test doubles for 'DbSet`1' must provide implementations of methods and properties that are used.
I want the call of create to fallback to the default implementation in DbSet.
Can someone help me with that?

After some struggle with the internal functions and async references of mocking a DbSet I came out with a helper class that solved most of my problems and might serve as base to someone implementation.
Here is the code:
public static class MockHelper
{
internal class TestDbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider {
private readonly IQueryProvider _inner;
internal TestDbAsyncQueryProvider(IQueryProvider inner) { _inner = inner; }
public IQueryable CreateQuery(Expression expression) { return new TestDbAsyncEnumerable<TEntity>(expression); }
public IQueryable<TElement> CreateQuery<TElement>(Expression expression) { return new TestDbAsyncEnumerable<TElement>(expression); }
public object Execute(Expression expression) { return _inner.Execute(expression); }
public TResult Execute<TResult>(Expression expression) { return _inner.Execute<TResult>(expression); }
public Task<object> ExecuteAsync(Expression expression, CancellationToken cancellationToken) { return Task.FromResult(Execute(expression)); }
public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken) { return Task.FromResult(Execute<TResult>(expression)); }
}
internal class TestDbAsyncEnumerable<T> : EnumerableQuery<T>, IDbAsyncEnumerable<T> {
public TestDbAsyncEnumerable(IEnumerable<T> enumerable) : base(enumerable) { }
public TestDbAsyncEnumerable(Expression expression) : base(expression) { }
public IDbAsyncEnumerator<T> GetAsyncEnumerator() { return new TestDbAsyncEnumerator<T>(this.AsEnumerable().GetEnumerator()); }
IDbAsyncEnumerator IDbAsyncEnumerable.GetAsyncEnumerator() { return GetAsyncEnumerator(); }
public IQueryProvider Provider { get { return new TestDbAsyncQueryProvider<T>(this); } }
}
internal class TestDbAsyncEnumerator<T> : IDbAsyncEnumerator<T> {
private readonly IEnumerator<T> _inner;
public TestDbAsyncEnumerator(IEnumerator<T> inner) { _inner = inner; }
public void Dispose() { _inner.Dispose(); }
public Task<bool> MoveNextAsync(CancellationToken cancellationToken) { return Task.FromResult(_inner.MoveNext()); }
public T Current { get { return _inner.Current; } }
object IDbAsyncEnumerator.Current { get { return Current; } }
}
public static Mock<TDbSet> CreateDbSet<TDbSet, TEntity>(IList<TEntity> data, Func<object[], TEntity> find = null)
where TDbSet : class, IDbSet<TEntity>
where TEntity : class, new() {
var source = data.AsQueryable();
var mock = new Mock<TDbSet> { CallBase = true };
mock.As<IQueryable<TEntity>>().Setup(m => m.Expression).Returns(source.Expression);
mock.As<IQueryable<TEntity>>().Setup(m => m.ElementType).Returns(source.ElementType);
mock.As<IQueryable<TEntity>>().Setup(m => m.GetEnumerator()).Returns(source.GetEnumerator());
mock.As<IQueryable<TEntity>>().Setup(m => m.Provider).Returns(new TestDbAsyncQueryProvider<TEntity>(source.Provider));
mock.As<IDbAsyncEnumerable<TEntity>>().Setup(m => m.GetAsyncEnumerator()).Returns(new TestDbAsyncEnumerator<TEntity>(data.GetEnumerator()));
mock.As<IDbSet<TEntity>>().Setup(m => m.Create()).Returns(new TEntity());
mock.As<IDbSet<TEntity>>().Setup(m => m.Add(It.IsAny<TEntity>())).Returns<TEntity>(i => { data.Add(i); return i; });
mock.As<IDbSet<TEntity>>().Setup(m => m.Remove(It.IsAny<TEntity>())).Returns<TEntity>(i => { data.Remove(i); return i; });
if (find != null) mock.As<IDbSet<TEntity>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns(find);
return mock;
}
public static Mock<DbSet<TEntity>> CreateDbSet<TEntity>(IList<TEntity> data, Func<object[], TEntity> find = null)
where TEntity : class, new() {
return CreateDbSet<DbSet<TEntity>, TEntity>(data, find);
}
}
And here is a use sample (based on the names I've given before):
var data = new List<DummyEntity> {
new DummyEntity { Value1 = "First", Value2 = "001" } },
new DummyEntity { Value1 = "Second", Value2 = "002" } }
};
var mockDummyEntities = MockHelper.CreateDbSet<DerivedDbSet<DummyEntities>, DummyEntities>(data, i => data.FirstOrDefault(k => k.Value2 == (string)i[0]));
var mockContext = new Mock<DummyDbContext>();
mockContext.Setup(c => c.DummyEntities).Returns(mockDummyEntities.Object);
Any suggestions on how to improve this solution is very welcome.
Regards

This is a modified version based on Andre that worked for me. Note, that I did not need the async references. Code will add all derived classes (if any)
Usage:
/// <summary>
///
/// </summary>
[TestMethod]
public void SomeTest()
{
//Setup
var mockContext = new Mock<FakeDbContext>();
//SomeClass can be abstract or concrete
mockContext.createFakeDBSet<SomeClass>();
var db = mockContext.Object;
//Setup create(s) if needed on concrete classes
//Mock.Get(db.Set<SomeOtherClass>()).Setup(x => x.Create()).Returns(new SomeOtherClass());
//DO Stuff
var list1 = db.Set<SomeClass>().ToList();
//SomeOtherClass derived from SomeClass
var subList1 = db.Set<SomeOtherClass>().ToList();
CollectionAssert.AreEquivalent(list1.OfType<SomeOtherClass>.ToList(), subList1);
}
Code:
/// <summary>
/// http://stackoverflow.com/questions/21943328/ef6-mocking-derived-dbsets
/// </summary>
public static class MoqSetupExtensions
{
static IEnumerable<Type> domainTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(x => x.GetTypes());
public static Mock<DbSet<T>> createFakeDBSet<T>(this Mock<FakeDbContext> db, List<T> list = null, Func<List<T>, object[], T> find = null, bool createDerivedSets = true) where T : class
{
list = list ?? new List<T>();
var data = list.AsQueryable();
//var mockSet = MockHelper.CreateDbSet(list, find);
var mockSet = new Mock<DbSet<T>>() { CallBase = true };
mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(() => { return data.Provider; });
mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(() => { return data.Expression; });
mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(() => { return data.ElementType; });
mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(() => { return list.GetEnumerator(); });
mockSet.Setup(m => m.Add(It.IsAny<T>())).Returns<T>(i => { list.Add(i); return i; });
mockSet.Setup(m => m.AddRange(It.IsAny<IEnumerable<T>>())).Returns<IEnumerable<T>>((i) => { list.AddRange(i); return i; });
mockSet.Setup(m => m.Remove(It.IsAny<T>())).Returns<T>(i => { list.Remove(i); return i; });
if (find != null) mockSet.As<IDbSet<T>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns<object[]>((i) => { return find(list, i); });
//mockSet.Setup(m => m.Create()).Returns(new T());
db.Setup(x => x.Set<T>()).Returns(mockSet.Object);
//Setup all derived classes
if (createDerivedSets)
{
var type = typeof(T);
var concreteTypes = domainTypes.Where(x => type.IsAssignableFrom(x) && type != x).ToList();
var method = typeof(MoqSetupExtensions).GetMethod("createFakeDBSetSubType");
foreach (var item in concreteTypes)
{
var invokeResult = method.MakeGenericMethod(type, item)
.Invoke(null, new object[] { db, mockSet });
}
}
return mockSet;
}
public static Mock<DbSet<SubType>> createFakeDBSetSubType<BaseType, SubType>(this Mock<FakeDbContext> db, Mock<DbSet<BaseType>> baseSet)
where BaseType : class
where SubType : class, BaseType
{
var dbSet = db.Object.Set<BaseType>();
var mockSet = new Mock<DbSet<SubType>>() { CallBase = true };
mockSet.As<IQueryable<SubType>>().Setup(m => m.Provider).Returns(() => { return dbSet.OfType<SubType>().Provider; });
mockSet.As<IQueryable<SubType>>().Setup(m => m.Expression).Returns(() => { return dbSet.OfType<SubType>().Expression; });
mockSet.As<IQueryable<SubType>>().Setup(m => m.ElementType).Returns(() => { return dbSet.OfType<SubType>().ElementType; });
mockSet.As<IQueryable<SubType>>().Setup(m => m.GetEnumerator()).Returns(() => { return dbSet.OfType<SubType>().GetEnumerator(); });
mockSet.Setup(m => m.Add(It.IsAny<SubType>())).Returns<SubType>(i => { dbSet.Add(i); return i; });
mockSet.Setup(m => m.AddRange(It.IsAny<IEnumerable<SubType>>())).Returns<IEnumerable<SubType>>((i) => { dbSet.AddRange(i); return i; });
mockSet.Setup(m => m.Remove(It.IsAny<SubType>())).Returns<SubType>(i => { dbSet.Remove(i); return i; });
mockSet.As<IDbSet<SubType>>().Setup(m => m.Find(It.IsAny<object[]>())).Returns<object[]>((i) => { return dbSet.Find(i) as SubType; });
baseSet.Setup(m => m.Create<SubType>()).Returns(() => { return mockSet.Object.Create(); });
db.Setup(x => x.Set<SubType>()).Returns(mockSet.Object);
return mockSet;
}
}

Microsoft published a very well explained guide providing an in-memory implementation of DbSet which has a complete implemention for all the methods on DbSet.
Check the article at http://msdn.microsoft.com/en-us/data/dn314431.aspx#doubles

QueryOver where generator Nhibernate

Hello i got some method that generating where statment programmatically how can i move where generation to other class method anyone can help ?
public static List<MME.Objects.TypedLists.InvoiceList> GetList(List<MMPFramework.SearchParameter> parameter)
{
MME.Objects.Invoice Invoice = null;
MME.Objects.Contractor Contractor = null;
MME.Objects.Contract Contract = null;
MME.Objects.TypedLists.InvoiceList invoiceList= null;
var t = MME.DAL.NhSessionHelper.GetCurrentSession().QueryOver<MME.Objects.Invoice>(() => Invoice);
foreach (var searchParameter in parameter)
{
if(searchParameter.Expression == "Like")
{
t.Where(Restrictions.Like(searchParameter.PropertyName, searchParameter.ObjectValueLo));
}
else if (searchParameter.Expression == "Eq")
{
t.Where(Restrictions.Eq(searchParameter.PropertyName, searchParameter.ObjectValueLo));
}
else if (searchParameter.Expression == "Between")
{
t.Where(Restrictions.Between(searchParameter.PropertyName, searchParameter.ObjectValueLo,searchParameter.ObjectValueHi));
}
else if(searchParameter.Expression == "Gt")
{
t.Where(Restrictions.Gt(searchParameter.PropertyName, searchParameter.ObjectValueLo));
}
else if (searchParameter.Expression == "Lt")
{
t.Where(Restrictions.Lt(searchParameter.PropertyName, searchParameter.ObjectValueLo));
}
else
{
//todo more
}
//t.Where(Restrictions.Eq(searchParameter.PropertyName, searchParameter.ObjectValue));
}
t.JoinQueryOver(() => Invoice.Contractor, () => Contractor, JoinType.LeftOuterJoin)
.JoinQueryOver(() => Invoice.Contract, () => Contract, JoinType.LeftOuterJoin)
.Select(Projections.Property(() => Invoice.Id).WithAlias(() => invoiceList.Id),
Projections.Property(() => Invoice.Number).WithAlias(() => invoiceList.InvoiceNumber),
Projections.Property(() => Contractor.Name).WithAlias(() => invoiceList.ContractorName),
Projections.Property(() => Contract.Number).WithAlias(() => invoiceList.ContractNumber)
)
.TransformUsing(Transformers.AliasToBean<MME.Objects.TypedLists.InvoiceList>());
return t.List<MME.Objects.TypedLists.InvoiceList>().ToList();
}
I've tried with this but it seems to not work.... Hope someone was doing something and can help me to handle with it.
public class BaseList
{
public object WhereGenerator(object ob)
{
QueryOver Ded = ob as QueryOver;
return null;
}
}

foreach (var restriction in BaseList.Createrestrictions(parameter))
{
t.Where(restriction);
}
public class BaseList
{
public IEnumerable<AbstractCriterion> Createrestrictions(List<MMPFramework.SearchParameter> parameter)
{
return parameter.Select(ToCritieria);
}
private AbstractCriterion ToCritieria(SearchParameter searchParameter)
{
if(searchParameter.Expression == "Like")
{
return Restrictions.Like(searchParameter.PropertyName, searchParameter.ObjectValueLo);
}
else ...
}
}

Is there idiomatic C# equivalent to C's comma operator?

I'm using some functional stuff in C# and keep getting stuck on the fact that List.Add doesn't return the updated list.
In general, I'd like to call a function on an object and then return the updated object.
For example it would be great if C# had a comma operator:
((accum, data) => accum.Add(data), accum)
I could write my own "comma operator" like this:
static T comma(Action a, Func<T> result) {
a();
return result();
}
It looks like it would work but the call site would ugly. My first example would be something like:
((accum, data) => comma(accum.Add(data), ()=>accum))
Enough examples! What's the cleanest way to do this without another developer coming along later and wrinkling his or her nose at the code smell?

I know this as Fluent.
A Fluent example of a List.Add using Extension Methods
static List<T> MyAdd<T>(this List<T> list, T element)
{
list.Add(element);
return list;
}

I know that this thread is very old, but I want to append the following information for future users:
There isn't currently such an operator. During the C# 6 development cycle a semicolon operator was added, as:
int square = (int x = int.Parse(Console.ReadLine()); Console.WriteLine(x - 2); x * x);
which can be translated as follows:
int square = compiler_generated_Function();
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private int compiler_generated_Function()
{
int x = int.Parse(Console.ReadLine());
Console.WriteLine(x - 2);
return x * x;
}
However, this feature was dropped before the final C# release.

You can do almost exactly the first example naturally using code blocks in C# 3.0.
((accum, data) => { accum.Add(data); return accum; })

This is what Concat http://msdn.microsoft.com/en-us/library/vstudio/bb302894%28v=vs.100%29.aspx is for. Just wrap a single item in an array. Functional code should not mutate the original data. If performance is a concern, and this isn't good enough, then you'll no longer be using the functional paradigm.
((accum, data) => accum.Concat(new[]{data}))

Another technique, straight from functional programming, is as follows. Define an IO struct like this:
/// <summary>TODO</summary>
public struct IO<TSource> : IEquatable<IO<TSource>> {
/// <summary>Create a new instance of the class.</summary>
public IO(Func<TSource> functor) : this() { _functor = functor; }
/// <summary>Invokes the internal functor, returning the result.</summary>
public TSource Invoke() => (_functor | Default)();
/// <summary>Returns true exactly when the contained functor is not null.</summary>
public bool HasValue => _functor != null;
X<Func<TSource>> _functor { get; }
static Func<TSource> Default => null;
}
and make it a LINQ-able monad with these extension methods:
[SuppressMessage("Microsoft.Naming", "CA1724:TypeNamesShouldNotMatchNamespaces")]
public static class IO {
public static IO<TSource> ToIO<TSource>( this Func<TSource> source) {
source.ContractedNotNull(nameof(source));
return new IO<TSource>(source);
}
public static IO<TResult> Select<TSource,TResult>(this IO<TSource> #this,
Func<TSource,TResult> projector
) =>
#this.HasValue && projector!=null
? New(() => projector(#this.Invoke()))
: Null<TResult>();
public static IO<TResult> SelectMany<TSource,TResult>(this IO<TSource> #this,
Func<TSource,IO<TResult>> selector
) =>
#this.HasValue && selector!=null
? New(() => selector(#this.Invoke()).Invoke())
: Null<TResult>();
public static IO<TResult> SelectMany<TSource,T,TResult>(this IO<TSource> #this,
Func<TSource, IO<T>> selector,
Func<TSource,T,TResult> projector
) =>
#this.HasValue && selector!=null && projector!=null
? New(() => { var s = #this.Invoke(); return projector(s, selector(s).Invoke()); } )
: Null<TResult>();
public static IO<TResult> New<TResult> (Func<TResult> functor) => new IO<TResult>(functor);
private static IO<TResult> Null<TResult>() => new IO<TResult>(null);
}
and now you can use the LINQ comprehensive syntax thus:
using Xunit;
[Fact]
public static void IOTest() {
bool isExecuted1 = false;
bool isExecuted2 = false;
bool isExecuted3 = false;
bool isExecuted4 = false;
IO<int> one = new IO<int>( () => { isExecuted1 = true; return 1; });
IO<int> two = new IO<int>( () => { isExecuted2 = true; return 2; });
Func<int, IO<int>> addOne = x => { isExecuted3 = true; return (x + 1).ToIO(); };
Func<int, Func<int, IO<int>>> add = x => y => { isExecuted4 = true; return (x + y).ToIO(); };
var query1 = ( from x in one
from y in two
from z in addOne(y)
from _ in "abc".ToIO()
let addOne2 = add(x)
select addOne2(z)
);
Assert.False(isExecuted1); // Laziness.
Assert.False(isExecuted2); // Laziness.
Assert.False(isExecuted3); // Laziness.
Assert.False(isExecuted4); // Laziness.
int lhs = 1 + 2 + 1;
int rhs = query1.Invoke().Invoke();
Assert.Equal(lhs, rhs); // Execution.
Assert.True(isExecuted1);
Assert.True(isExecuted2);
Assert.True(isExecuted3);
Assert.True(isExecuted4);
}
When one desires an IO monad that composes but returns only void, define this struct and dependent methods:
public struct Unit : IEquatable<Unit>, IComparable<Unit> {
[CLSCompliant(false)]
public static Unit _ { get { return _this; } } static Unit _this = new Unit();
}
public static IO<Unit> ConsoleWrite(object arg) =>
ReturnIOUnit(() => Write(arg));
public static IO<Unit> ConsoleWriteLine(string value) =>
ReturnIOUnit(() => WriteLine(value));
public static IO<ConsoleKeyInfo> ConsoleReadKey() => new IO<ConsoleKeyInfo>(() => ReadKey());
which readily allow the writing of code fragments like this:
from pass in Enumerable.Range(0, int.MaxValue)
let counter = Readers.Counter(0)
select ( from state in gcdStartStates
where _predicate(pass, counter())
select state )
into enumerable
where ( from _ in Gcd.Run(enumerable.ToList()).ToIO()
from __ in ConsoleWrite(Prompt(mode))
from c in ConsoleReadKey()
from ___ in ConsoleWriteLine()
select c.KeyChar.ToUpper() == 'Q'
).Invoke()
select 0;
where the old C comma operator is readily recognized for what it is: a monadic compose operation.
The true merit of the comprehension syntax is apparent when one attempts to write that fragment in the flunt style:
( Enumerable.Range(0,int.MaxValue)
.Select(pass => new {pass, counter = Readers.Counter(0)})
.Select(_ => gcdStartStates.Where(state => _predicate(_.pass,_.counter()))
.Select(state => state)
)
).Where(enumerable =>
( (Gcd.Run(enumerable.ToList()) ).ToIO()
.SelectMany(_ => ConsoleWrite(Prompt(mode)),(_,__) => new {})
.SelectMany(_ => ConsoleReadKey(), (_, c) => new {c})
.SelectMany(_ => ConsoleWriteLine(), (_,__) => _.c.KeyChar.ToUpper() == 'Q')
).Invoke()
).Select(list => 0);

The extension method is arguably the best solution, but for completeness' sake, don't forget the obvious alternative: a wrapper class.
public class FList<T> : List<T>
{
public new FList<T> Add(T item)
{
base.Add(item);
return this;
}
public new FList<T> RemoveAt(int index)
{
base.RemoveAt(index);
return this;
}
// etc...
}
{
var list = new FList<string>();
list.Add("foo").Add("remove me").Add("bar").RemoveAt(1);
}

I thought it would be interesting to make a version of my wrapper class answer that doesn't require you write the wrapper methods.
public class FList<T> : List<T>
{
public FList<T> Do(string method, params object[] args)
{
var methodInfo = GetType().GetMethod(method);
if (methodInfo == null)
throw new InvalidOperationException("I have no " + method + " method.");
if (methodInfo.ReturnType != typeof(void))
throw new InvalidOperationException("I'm only meant for void methods.");
methodInfo.Invoke(this, args);
return this;
}
}
{
var list = new FList<string>();
list.Do("Add", "foo")
.Do("Add", "remove me")
.Do("Add", "bar")
.Do("RemoveAt", 1)
.Do("Insert", 1, "replacement");
foreach (var item in list)
Console.WriteLine(item);
}
Output:
foo
replacement
bar
EDIT
You can slim down the syntax by exploiting C# indexed properties.
Simply add this method:
public FList<T> this[string method, params object[] args]
{
get { return Do(method, args); }
}
And the call now looks like:
list = list["Add", "foo"]
["Add", "remove me"]
["Add", "bar"]
["RemoveAt", 1]
["Insert", 1, "replacement"];
With the linebreaks being optional, of course.
Just a bit of fun hacking the syntax.