.net - Performance Implications Of Implementing A Generic Type And A Delegate In A Function?
Aug 4, 2010
I wrote a serializer (to Byte Array) for dictionaries that have a string key, but an object of some sort as its value.I've never implemented a generic type in a function or used a delegate before, so I'm a bit concerned about this being significantly slower than writing a serialization function for a specific type of Dictionary (Dictionary(Of String, MyClass) for example)Should this code be significantly slower due to the use of the generic type or the delegate?
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It works, and I could loop it and compare it to a more static Dictionary serializer, but I'm more concerned about when I start using this for a lot of different String/Object dictionary combinations, and it'll take me a long time to write a bunch of static dictionary serializers (that's what I'm hoping to avoid in the first place)edit: simplified intro text
D is a dictionary whose entry values are of Type T..What I'm attempting to do is have a delegate like "Serializer" below that I can invoke on an instance of T, such as "Entry.Value" below.Please see the "return Entry..." line below for my wishful thinking.[code]
I'm implementing a poor-man's ORM an a legacy application (.NET 2.0 web app, hand-coded SQL queries). I have two data classes: Customer and Order:
Public Class Customer Public Property CustomerId As Integer Public Property CustomerName As String
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I'm concerned about the performance of this method, namely if I'm pulling multiple Customer's. For each Customer pulled, I have to hit the database again (opening another connection), and getting the orders for that given customer. If I'm not mistaking, it wouldn't take many records to accumulate a large number of open connections.
How can I determine the number of new connections being made and whether or not I'll encounter any connection pooling or other such .NET-imposed limits?
One thought I've had is to pass the SQLConnection object created in the calling class to the getOrdersByCustomerId function and have that function use the (apparently?) already-open connection. I have not tested it namely because I don't know how to determine if it's better than my existing method. Thoughts?
I'm creating a search web service that returns JSON for processing by the client. The service takes a single search parameter, performs multiple lookups on different tables, then returns a custom JSON object. For example, if the user puts in what appears to be a name, I search both the Customers table for a list of the top n customers and the Orders table for the top n orders that have a customer with that name.
Currently I have written a function to deserialize XML as seen below.How do I change it so I don't have to replace the type every time I want to serialize another object type ? The current object type is cToolConfig. How do I make this function generic ?
Public Shared Function DeserializeFromXML(ByRef strFileNameAndPath As String) As XMLhandler.XMLserialization.cToolConfig Dim deserializer As New System.Xml.Serialization.XmlSerializer(GetType(cToolConfig)) Dim srEncodingReader As IO.StreamReader = New IO.StreamReader(strFileNameAndPath, System.Text.Encoding.UTF8) Dim ThisFacility As cToolConfig
I would like to write a generic function that would search a List(Of T) for all elements of type TFilter and return a List(Of TFilter) which comprises those elements.
I've tried this: Public Function FilterList(Of T, TFilter)(ByVal ListToFilter As List(Of T)) As List(Of TFilter) Return ListToFilter.FindAll(Function(z) z.GetType.Equals(GetType(TFilter))).ConvertAll(New Converter(Of T, TFilter)(Function(z) CType(z, TFilter))) End Function
But, it gives the following error: Value of type 'T' cannot be converted to 'TFilter'.
MsgBox(AddSomething(Of String)("Hello", "World")) Public Function AddSomething(Of T)(ByVal FirstValue As T, ByVal SecondValue As T) As String Return FirstValue.ToString + SecondValue.ToString
Suppose I want to write a generic function that will return the fully qualified name of the data type. In other words, how would you implement the following: Public Shared Function Foo(Of T)() As String ' Return the fully qualified name of T End Function
The idea is to expand on the existing, old, and lacking Inputbox, to allow for:1. A greater variety of types (Integers, doubles, List(Of String), etc.2. Data validation.For example, if the user wants the user to quickly enter an Integer, I want a custom Inputbox form to show up with a TextBox, which only allows Integer input. If he wants the user to choose from a List(Of String), I show a form with a Combobox instead, from which the user can then choose.
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As T Dim queryStringObject As Nullable(Of T) = Nothing If queryStringVariable <> Nothing Then If HttpContext.Current.Request.QueryString(queryStringVariable) IsNot Nothing Then queryStringObject = DirectCast(HttpContext.Current.Request.QueryString(queryStringVariable), T) End If
I wrote my own database handling code (actually, I write T4 text templating files that generate my database code for me) and part of it takes care of converting values from a database (as Objects) to the desired types.
I have been using this generic function successfully:
vb.net Public Overridable Function ConvertType(Of T)(value As Object) As T Try Return If(value IsNot Nothing AndAlso value <> DBNull.Value, DirectCast(value, T), Nothing)
[Code]....
Simple enough, but it doesn't work... The return type of the function is (and must be) T, so I cannot return a Boolean because a Boolean cannot be converted to T!
Well... It can in this case, because I specifically check that T is Boolean, but the compiler doesn't know this so it doesn't allow me to return a Boolean. I cannot cast the boolean to T either.
I wrote my own database handling code (actually, I write T4 text templating files that generate my database code for me) and part of it takes care of converting values from a database (as Objects) to the desired types. I have been using this generic function successfully:
vb.net Public Overridable Function ConvertType(Of T)(value As Object) As T Try
I am trying to create a class implementing the generic IComparer of my own class "Stellungen" (which translates to positions, like on a chess or checkers board).
This is what I got: Private Class comparer(Of Stellung) Implements System.Collections.Generic.IComparer(Of Stellung) Public Function Compare(x As Stellung, y As Stellung) As Integer Implements System.Collections.Generic.IComparer(Of Stellung).Compare End Function End Class
Problem is: inside the function I have no access to any fields of my class. If I start off with x. Intellisense will only give me .Equals, .GetHashCode - the methods you get on a type but not on an instance. Visual Studio 10 also highlights this, in the definition of the function the bits "x as Stellung" and "y as Stellung" are written in light blue, meaning it is a type and not an actual object. How do I access the things I want to compare inside my class?
I am creating a generic class that is Implementing IList(Of T) which requires that I implement the GetEnumorator of both IEnumerable(Of T) and IEnumerable. When looking at the members of IList(Of T) I see only one GetEnumorator function, yet it implements IEnumerable(Of T) and IEnumerable. How can I use one function to implement both interfaces when the function definitions only vary by return type?
In our current project I am using a generic interface iService which is inherited by all other service interfaces. For instance IService is inherited by ILogService.
The ILogService interface is then implemented by LogService as below:
Public Interface IService(Of T) Sub Save(ByVal T As IEntity) Sub Remove(ByVal T As IEntity)
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How can I update the method signature so T is displayed as Log?
Public MustInherit Class Column Public ReadOnly Property ReturnSomethingUseful() As Object Get 'return something useful
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But this gives the following error:
Public Overrides Function ParseValue(sValue As String) As Boolean' cannot override 'Public Overridable Function ParseValue(sValue As String) As Object' because they differ by their return types.
I accept that you can't do this, but I'd like to be able to preserve the semantics of what I'm. trying to do, which is to have an untyped version that deals with Object, but a typed version in derived classes that knows about the specific type T.
Scroll to the bottom, EDIT 19 onwards. See @Chris's comments also for good examples
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It's all gone quiet since Edit 19ish and @Chris reinforcing the issue with a good example (thank you Chris). I'll make the question a little easier (and attempt to tidy up all of the above), can anyone prove this is not an MS bug or similar? It seems to be something under the hood is not correctly wired up for VB.Net with regards to Nullable Structures and Events? However, all other cases using the Nullable Structures does appear to work?
I'm trying to search a generic list of 'User' business objects which has a property called 'Username': If (From u In colUsers Select u.Username Where Username.Equals(strUsername)).Count > 0 ThenI keep getting:Delegate to an instance method cannot have null 'this'.
public delegate UsernameCredentials UsernameRequiredEventHandler( object sender, string endpoint ); public event UsernameRequiredEventHandler UsernameRequired;
On Converting the above code in VB.Net as follow :
Public Delegate Function UsernameRequiredEventHandler(ByVal sender As Object, ByVal endpoint As String) As UsernameCredentials Public Event UsernameRequired As UsernameRequiredEventHandler
I am getting error on the above line saying that "Events cannot be declared with a delegate type that has a return type".I understand that this is not supported in VB.Net.
I am trying to create a list of a generic type in vb.net 2.0 framework. This is the generic type definition:
Public Class GenericParamMap(Of T) Public Sub New(ByVal pParamName As String, ByVal pPropValue As T) mParamName = pParamName
[Code]....
The compiler does not allow a "T" in the method's parameter because it's not defined, but I'm not sure how or where to define it. I thought it was okay to have a generic method definition.
I am trying to write a generic method, to avoid code duplication, which will create or activate a Form as an MDI children, based on its type. But I have to lines in error (see comments).
im trying to implement a search function to my booking program, wich retrieves data from a SQL database. I have the screan all set up and all the variables at the ready, the only problem is, im not sure how to execute it in a sqlcommand line.
I've got all the fields that are required, such as date, time but i also have two optional options, Room Type and Room Capacity.
How would i write a sqlcommand to search for available rooms that meet the criteria for the room to be booked?
I'm fairly new to VB and am having trouble implementing the Round function. I know that the syntax for what I'm trying to do is:document.write(Round("KwH",2))But my problem is that I can't get it working with the following line:.Kwh = items.Attribute("KwH").Value _So I want the output of whatever 'KwH' spits out to have only 2 decimals, despite the actual figure having 8
I'm compiling a VB.Net 2.0 app (created in VS2008) using msbuild, and now I've added a generic return type, it's giving me the following:
Warning: Type library exporter encountered a generic type instance in a signature. Generic code may not be exported to COM.
Having just spent ages removing all of the previous warnings, I don't really want to add a new one. Any idea how to get rid of it (aside from not using generics)?I don't know what details I'd put in the attribute, or what number to put in the project-level ignore list.
I have a generic Class I'm using to hold information loaded from a database.I have a method which takes a DataRow as an argument, uses the object's known column name and extracts the data from the DataRow, such that:Dim loadData As T = CType(myDataRow("myColumnName"), T))works as my default assignment in most cases.Unfortunately, due to some horrifying design constraints, some of my columns may be null, and may also be taken from enumerations.This means that when <T> is Nullable(Of SomeEnumeration) the above code does not work because I can't cast 0 directly to SomeEnumeration.Zero.Is there some way to check whether <T> is Nullable(Of [Enum])? Or some way to write a method which allows Integers to be cast to Nullable(Of [Enum])?I feel like I'm forgetting something that would allow me to write one of the other of these, but my weak google-fu is turning up nothing.
EDIT: Okay, thanks to dasblinkenlight's answer below, I can detect when this circumstance is occurring, but what I need to do now is to take a type <T> which I know is Nullable(Of SomeClass), get a type reference to SomeClass and then create a new object of type Nullable(Of SomeClass) and assign that to LoadData.My problem was that I had a lot of difficulty in finding any function which would accept baseType as an actual Type.Parse accepted baseType as a parameter, I knew baseType was an [Enum] type because of dasblinkenlight's code, so I was, in this instance, able to code a solution. It's a solution which is very specific to my problem (i.e., T is Nullable(of SomeEnumeration)), but it's a solution nonetheless.
I'm currently trying to create a class that is a composition of the SqlDataAdapter class (as unfortunately you can't inherit from it). In order to try and make it as similar as possible I'm using all the same inherits and interfaces as is documented on MSDN.The problem that I am having is that there are some properties where the interface specifies that the type of the property is IDbCommand. But in the SqlDataAdapter the property type is SqlCommand.
In trying to add a bit of usage variety to a generic class I'm working on, I ran into this issue with trying to cast an object into an interface instance where the interface is defined inside the generic class.
1) VB Allows non-type template parameters2) VB supports explicit specialization 3) VB allows the type parameters to be used as the base class for the generic type4) VB allows a generic type parameter itself to to be a generic 5) VB enforces that all codes are valid for all types of parametrs
