Include A Generic Type Parameter In A Lamba Expression (2010)?
Jun 25, 2010
(Not really sure if I phrased the question correctly...) I want to create a lambda expression that would take an Object, attempt to convert it to a passed-in Type, and print to the console whether it was successful or not. At a glance, the lambda expression may seem a pretty silly way to accomplish this task, but I'd really like to know what I'm doing wrong, so I can better grow my skill set.
VS gives me a designer error about the second "T" in the expression below, telling me it isn't defined) This is where I left off:
[Code]...
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Feb 7, 2011
Can someone explain what lambda expressions are?
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Dec 23, 2011
The following code produces the compiler error "Expression expected" (Sub is underlined).
Dim lambda As Action(Of Integer) = Sub(x) Console.WriteLine(x)
Why does this not work?
Note: The corresponding C# code works:
Action<int> lambda = x => Console.WriteLine(x);
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Nov 19, 2010
lambda - vb.net lamba expression to select all values between lower and upper values plus the next lower and upper value. I need some help with a lamda expression to get a subset of range of values. I have a lower and upper value, and getting everything between them seems easy enough, but I also need the next lower and higher value to be included. I can do each of these separately, but would like to do it in one shot if possible.
The range I need the subset from has 150 values. A small example would look like:
{8.206,8.206,8.201,8.196,8.193,8.192,8.189,8.174,8.171,8.171,8.166,8.163,8.157,8.154,8.153,8.14,8.131}
My lower value is: 8.16
My upper value is: 8.17
I need to get back: {8.171,8.171,8.166,8.163,8.157}
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Mar 3, 2011
I have the following VB.NET function, for example:
Public Function MyFunction (Of TData) (ByVal InParam As Integer) As TData
End Sub
How do I, in a function, determine if TData is a NULLable Type?
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Feb 14, 2011
say I have two POCOs I'm using in EF code first
Public class C1
property F1 as integer
End Class
Public class C2
property F2 as String
End Class
I want to have a function that will create a list either of C1 or C2, to be used in some generic operation, such that
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Jan 23, 2009
I have bee trying to figure out, how to match generic types, without the type parameter in a IF-ELSE statement - heres what i mean:
<P>IF TypeOf(Obj) Is GenericTypeExample(Of ???Any???) Then</P>
<P>End if</P>
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Feb 21, 2011
Anyone know a good workaround for the lack of an enum generic constraint?[cod]e...
Is is possible to limit the generic type parameter [I don't know if that's the right name] to an Enum?[code]...
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Jan 1, 2010
I use this code. USED CODE
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Mar 22, 2012
I want to pass an optional parameter to a function of type System.Drawing.Color. The problem I am having is that when I declare the function it says "Constant expression is required" but I have tried variations of the following, including integers, full qualified indentifiers, even old vbWhite constants to no avail.
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Apr 13, 2012
Consider:
Public MustInherit Class Column
Public ReadOnly Property ReturnSomethingUseful() As Object
Get
'return something useful
[code]....
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.
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Aug 1, 2011
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.
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Aug 19, 2009
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
[code].....
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Aug 14, 2010
I have a Journal that records entries for different types: Journal(Of ParentT)
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Mar 30, 2011
So that error doesn't really make since. I mean I know what the error means but my query looks good and is what I expected.Is there any way to see the final outcome from SQLInsert. Parameters.AddWithValue..Before it gets to "SQLInsert.ExecuteNonQuery()" ??
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Feb 27, 2012
I've got the following code to search for data from my database, but when I run the code its giving me a 'Data type mismatch in criteria expression.' but I cant for the life of me work out why
To fill my table I use: OleDbDataAdapter1.Fill(TAS_DataDataSet)
Then use the following to try and search for data by the employee ID;
Private Sub comboEmployee_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles comboEmployee.SelectedIndexChanged
Dim EmployeeID, SQLString As String
[Code]....
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Oct 10, 2009
I am making a GUI for ffmpeg. And i want a own namespace for it. So you can ex. write in Form1.vb:
ffmpeg.Execute("The command to execute")
or
ffmpeg.SetType.CBR
But i can't get it to work.This is what i have:
Imports System.IO
Namespace ffmpeg
Public Class Execute
[code]....
In the execute option, it gives me an error of Execute is a type in ffmpeg, not an expression.In the SetType thing, the two subs doesn't even come up when i call it.
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Jun 30, 2011
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.
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Feb 8, 2012
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).
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Mar 9, 2011
I want to have a "template" function that can receive different parameter and a type parameter, like:[code]But Vb told me that tupeList is not defined... is there a way I can do that?
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May 5, 2009
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.
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Sep 12, 2011
I have a question about ASP.Net, visual basic I have 2 LINQ query's, the first one works, the second one doesnt, produces a
"Unable to cast object of type 'System.Data.Objects.ObjectQuery'1[SelmaV2.Products]' to type 'System.Collections.Generic.List'1[System.String]'.
[Code]....
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Dec 14, 2011
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.
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Feb 14, 2012
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.
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Mar 30, 2010
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
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Jul 1, 2009
I am working on an application in Visual Basic Express using an Access 2000 database.I am trying to get athe following SQL query to work but get an error in Access.
The query is:
SELECT [ID], [Title], [Author], [Series], [YearPublished], [ISBN], [CoverPrice], [Style], [Condition], [Signed], [Comments], Count([Title]) AS CountOfBooks, Sum([CoverPrice]) AS TotalCoverPrice
FROM tblBooks
WHERE ID=[@ID];
The error is:"You have tried to execute a query that does not include the spec ified expression 'ID' as a part of the aggragate function."
The query works fine without the 'Count' and 'CoverPrice' count and sum to the query.
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Dec 22, 2009
E.g. how do I get VB.Net to statically type a local variable to be the static type of the expression on the right had side of the assignment?
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May 27, 2009
Is there a way you can do this ? I would like to have a collection class of T that would be able to do addition, substraction on the T type. I would like to keep T generic instead of having couple collections with the same code, but different types. How would you constrain the generic T?
Example: I would like to define a Collection(of T as IDoMaths). I wouldn't like to create my own integer etc classes with named methods to do the operations, because I think it would be slower. This part of the code is actually called very often and tends to be the bottleneck in performance.
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Jun 7, 2011
I have a storedproc accepts parameters in XMLtype as
CREATE OR REPLACE PROCEDURE GetDetails(
p_para IN XMLTYPE,
[code].....
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Feb 12, 2011
I'm using SharpZipLib to compress files. The library is wrapped in a plugin interface, in a separate DLL. I pass the plugin dll a ByRef parameter to keep track of the compression progress.SharpZipLib, while compressing, will periodically call a delegate sub passed when launching the compression. I can't figure out how to update the ByRef parameter when the delegate is called. If I try to assign the ByRef variable in the body of a lamba expression, I get a 'ByRef' parameter '<parametername>' cannot be used in a lambda expression error.
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