1. Expressions и все-все-все

2. http://sane.habrahabr.ru
http://der-waldgeist.blogspot.com
http://twitter.com/AlexSane
http://www.google.com/profiles/shurickFomin
http://crew.taucraft.com/

3. Expression
…остальные trees
плюшки
Expression
Visitor

5. 2+3*4
2+(3*4)

6. private static void Main()
{
Func<int, int, int> f = (x, y) => x + y;
Console.WriteLine(f);
}
System.Func`3[System.Int32,System.Int32,System.Int32]
[CompilerGenerated]
private static int <Main>b__0(int x, int y)
{
return x+y;
}
private static void Main()
{
var f = new Func<int, int, int>(Program.<Main>b__0));
Console.WriteLine(f);
}

7. static void Main()
{
Expression<Func<int, int, int>> f = (x, y) => x + y;
Console.WriteLine(f);
}
(x, y) => (x + y)
ParameterExpression CS0 = Expression.Parameter(typeof (int), "x");
ParameterExpression CS1 = Expression.Parameter(typeof (int), "y");
Expression<Func<int, int, int>> f =
Expression.Lambda<Func<int, int, int>>(
Expression.Add(CS0, CS1),
new ParameterExpression[] {CS0, CS1}
);

8. Expression<Func<DateTime, int>> f =
d => (int) Math.Abs((DateTime.Now - d).TotalSeconds);

9. d => (int) Math.Abs((DateTime.Now - d).TotalSeconds);
ParameterExpression CS0 = Expression.Parameter(typeof (DateTime), "d");
Expression<Func<DateTime, int>> f =
Expression.Lambda<Func<DateTime, int>>(
Expression.Convert(
Expression.Call(
null,
(MethodInfo) methodof (Math.Abs),
new Expression[]
{
Expression.Property(
Expression.Subtract(
Expression.Property(null, (MethodInfo) methodof (DateTime.get_Now)),
CS0,
(MethodInfo) methodof (DateTime.op_Subtraction)
),
(MethodInfo) methodof (TimeSpan.get_TotalSeconds)
)
}
), typeof (int)
), new ParameterExpression[] {CS0} );

10. Expression
tree

11. d => (int) Math.Abs((DateTime.Now - d).TotalSeconds);

12. .NET 3.0 .NET 4.0
• Operators • Blocks
• Method calls • Loops
• Property getters • Try/Catch/Finally
• Collection initializers • Goto/Labels
• Object initializers • Variables
• Convert/Cast • Assignments
• Constants • If/Then/Else
(x,y)=>x+y (x,y) => { return x+y; }*

14. ExpressionVisitor

15. protected virtual Expression VisitBinary(BinaryExpression b)
{
Expression left = this.Visit(b.Left);
Expression right = this.Visit(b.Right);
return b;
}

16. protected virtual Expression VisitBinary(BinaryExpression b)
{
Expression left = this.Visit(b.Left);
Expression right = this.Visit(b.Right);
if (left != b.Left || right != b.Right)
{
return Expression.MakeBinary(
b.NodeType, left, right, b.Method
);
}
return b;
}

22. IQueryable<Tree> forest = // ...
var queryable = from tree in forest
where tree.HasHollow
select tree.ColectSomeHoney();
var queryable = forest.Where(tree => tree.HasHollow)
.Select(tree => tree.ColectSomeHoney());
var queryable = Queryable.Select(
Queryable.Where(forest, tree => tree.HasHollow),
tree => tree.ColectSomeHoney() );
var queryable = Enumerable.Select(
Enumerable.Where(forest.AsEnumerable (), tree => tree.HasHollow),
tree => tree.ColectSomeHoney() );

23. internal override Expression VisitMethodCall(MethodCallExpression m)
{
Expression instance = base.VisitMethodCall(m);
if (m.Method.DeclaringType == typeof(Queryable))
{
MethodInfo info = FindEnumerableMethod(m.Method);
return Expression.Call(instance, info, source);
}
return m;
}

24. internal override Expression VisitMethodCall(MethodCallExpression m)
{
Expression instance = base.VisitMethodCall(m);
if (m.Method.DeclaringType == typeof(Queryable))
{
MethodInfo info = FindEnumerableMethod(m.Method);
return Expression.Call(instance, info, source);
}
return m;
}

27. Compiled expressions
string PasswordPhrase(bool isBear)
{
return string.Format("{0} очень любит {1}",
isBear ? "Мишка" : "Ослик",
isBear ? "мёд" : "йод");
}

28. ILGenerator generator = //...
var label1 = generator.DefineLabel();
var label2 = generator.DefineLabel();
var label3 = generator.DefineLabel();
var label4 = generator.DefineLabel();
generator.Emit(OpCodes.Ldstr, "{0} очень любит {1}");
generator.Emit(OpCodes.Ldarg_1);
generator.Emit(OpCodes.Brtrue_S, label1);
generator.Emit(OpCodes.Ldstr, "Мишка");
generator.Emit(OpCodes.Br_S, label2);
generator.MarkLabel(label1);
generator.Emit(OpCodes.Ldstr, ”Ослик");
generator.MarkLabel(label2);
generator.Emit(OpCodes.Ldarg_1);
generator.Emit(OpCodes.Brtrue_S, label3);
generator.MarkLabel(label3);
generator.Emit(OpCodes.Ldstr, ”мёд");
generator.Emit(OpCodes.Br_S, label4);
generator.Emit(OpCodes.Ldstr, "йод");
generator.MarkLabel(label4);
generator.EmitCall(OpCodes.Call, typeof(String).GetMethod("Format"), new[] { typeof(string), typeof(ob
ject), typeof(object) });
generator.Emit(OpCodes.Ret);

29. Func<bool, string> Emit()
{
var isBear = Expression.Parameter(typeof (bool), "isBear");
var lambda = Expression.Lambda<Func<bool, string>>(
Expression.Call(
Method(() => string.Format("", null, null)),
Expression.Constant("{0} очень любит {1}"),
Expression.Condition(isBear, Expression.Constant("Мишка"),
Expression.Constant("Ослик")),
Expression.Condition(isBear, Expression.Constant("мёд"), Expression.C
onstant("йод") )
)
);
Func<bool, string> func = lambda.Compile();
return func;
}

30. Reflection in compile time
public class Tree
{
public Honey ColectSomeHoney()
{
//...
return new Honey();
}
}
private static void Main()
{
MethodInfo method =
typeof(Tree).GetMethod( "ColectSomeHoney",
BindingFlags.Public | BindingFlags.Instance
);
}

31. Reflection in compile time
public class Tree
{
public Honey CollectSomeHoney()
{
//...
return new Honey();
}
}
private static void Main()
{
MethodInfo method =
typeof(Tree).GetMethod( "ColectSomeHoney",
BindingFlags.Public | BindingFlags.Instance
);
}

32. Reflection in compile time
public class Tree
{
public Honey CollectSomeHoney()
{
//...
return new Honey();
}
}
private static void Main()
{
MethodInfo method =
typeof(Tree).GetMethod( "ColectSomeHoney",
BindingFlags.Public | BindingFlags.Instance
);
}

33. Reflection in compile time
private static void Main()
{
var method = GetMethod<Tree>(x => x.ColectSomeHoney());
}
public static MethodInfo GetMethod<T>(Expression<Action<T>> e)
{
return ((MethodCallExpression) e.Body)
.Method;
}

34. Reflection in compile time
private static void Main()
{
var method = GetMethod<Tree>(x => x.CollectSomeHoney());
}
public static MethodInfo GetMethod<T>(Expression<Action<T>> e)
{
return ((MethodCallExpression) e.Body)
.Method;
}

35. IQueryable
interface IQueryable<T> : IEnumerable<T> , IQueryable
{
Type ElementType { get; }
Expression Expression { get; }
IQueryProvider Provider { get; }
}
interface IQueryProvider
{
IQueryable CreateQuery(Expression e) ;
IQueryable<T> CreateQuery<T> (Expression e);
object Execute (Expression expression);
object Execute (Expression expression);
}

36. IQueryable

38. Expressions в C# — impress yourself!
http://habrahabr.ru/blogs/net/83169/

39. LINQ: Building an IQueryable provider
series
http://blogs.msdn.com/b/mattwar/archive/2008/11/18/linq-links.aspx

40. Винни-Пух и Все-Все-все
ISBN: 978-5-17-064151-2