I have the following code: string prefix = "OLD:"; Func<string, string> prependAction = (x => prefix + x); prefix = "NEW:"; Console.WriteLine(prependAction("brownie")); Because the compiler replaces the prefix variable with a closure "NEW:brownie" is printed to the console. Is there an easy way to prevent the compiler from lifting th...
What is the best way of dynamically writing LINQ queries and Lambda expressions? I am thinking of applications where the end user can design business logic rules, which then must be executed. I am sorry if this is a newbie question, but it would be great to get best practices out of experience. ...
Backstory: I'm using log4net to handle all logging for a project I'm working on. One particular method can be called under several different circumstances -- some that warrant the log messages to be errors and others that warrant the log messages to be warnings. So, as an example, how could I turn Public Sub CheckDifference(ByVal A As...
Not sure if this is possible or if I'm expressing correctly what I'm looking for, but I have the following piece of code in my library repeatedly and would like to practice some DRY. I have set of SQL Server tables that I'm querying based on a simple user-supplied search field ala Google. I'm using LINQ to compose the final query based ...
I mostly use lambda functions but sometimes use nested functions that seem to provide the same behavior. Here are some trivial examples where they functionally do the same thing if either were found within another function: Lambda function >>> a = lambda x : 1 + x >>> a(5) 6 Nested function >>> def b(x): return 1 + x >>> b(5) 6 ...
I'm looking to create an ValidationRule class that validates properties on an entity type object. I'd really like to set the name of the property to inspect, and then give the class a delegate or a lambda expression that will be evaluated at runtime when the object runs its IsValid() method. Does anyone have a snippet of something like...
Could someone provide a good description of what a Lambda is? We have a tag for them and they're on the secrets of C# question, but I have yet to find a good definition and explanation of what they are in the first place. ...
If I have variable of type IEnumerable<List<string>> is there a LINQ statement or lambda expression I can apply to it which will combine the lists returning an IEnumerable<string>? ...
In a question answer I find the following coding tip:- 2) simple lambdas with one parameter: x => x.ToString() //simplify so many calls As someone who has not yet used 3.0 I don't really understand this tip but it looks interesting so I would appreciate an expantion on how this simplifies calls with a few examples. I've researched l...
I understand what are lambda functions in Python, but I can't find what is the meaning of "lambda binding" by searching the Python docs. A link to read about it would be great. A trivial explained example would be even better. Thank you. ...
I have quickly read the Microsoft Lambda Expression documentation. I see example that have help me to understand more like this one : delegate int del(int i); del myDelegate = x => x * x; int j = myDelegate(5); //j = 25 But, I still do not understand why it's so an innovation. It's just a method that die when the "method variable" en...
I don't really get lambda expressions. While they've been around since the days of ALGOL, I didn't start hearing about them until fairly recently, when Python and Ruby became very popular. Now that C# has the => syntax, people in my world (.NET) are talking about lamdba expressions more and more. I've read the Wikipedia article on the ...
So .NET 3.0/3.5 provides us with lots of new ways to query, sort, and manipulate data, thanks to all the neat functions supplied with LINQ. Sometimes, I need to compare user-defined types that don't have a built-in comparison operator. In many cases, the comparison is really simple -- something like foo1.key ?= foo2.key. Rather than c...
I'm using C# on Framework 3.5. I'm looking to quickly sort a Generic List<>. For the sake of this example lets say I have a List of a Person type with a property of lastname. How would I sort this List using a lambda expression? List<Person> people = PopulateList(); people.OrderBy(???? => ?????) ...
I want to be able to write a lambda/Proc in my Ruby code, serialize it so that I can write it to disk, and then execute the lambda later. Sort of like... x = 40 f = lambda { |y| x + y } save_for_later(f) Later, in a separate run of the Ruby interpreter, I want to be able to say... f = load_from_before z = f.call(2) z.should == 42 ...
I have these two pieces of code, wich one is more readable? foreach decimal technicalPremium = 0; foreach (Risk risk in risks) { technicalPremium = technicalPremium + risk.TechnicalPremium; } return technicalPremium; linq return risks.Sum(risk => risk.TechnicalPremium); ...
I believe the following VB.Net code is the equivalent of the proceeding C# code; however the VB.Net test fails - the event handling Lambda is never called. What is going on? VB.Net version - fails: <TestFixture()> _ Public Class TestClass <Test()> _ Public Sub EventTest() Dim eventClass As New EventClass Dim ev...
I am just now learning about function pointers and as I was readying the K&R chapter on the subject the first thing that hit me was, "Hey, this is kinda like a closure." I knew this assumption is fundamentally wrong somehow and after a search online wasn't really to find any analysis of this comparison. So why are C style function point...
What reason is there for C# or java having lambdas? Neither language is based around them, it appears to be another coding method to do the same thing that C# already did. I'm not being confrontational, if there is a reason I would like to know the reason why. For the purpose of full disclosure I am a Java programmer with a C++ backgroun...
I have an s-expression bound to a variable in Common Lisp: (defvar x '(+ a 2)) Now I want to create a function that when called, evaluates the expression in the scope in which it was defined. I've tried this: (let ((a 4)) (lambda () (eval x))) and (let ((a 4)) (eval `(lambda () ,x))) But both of these create a problem: EVAL...