I have a huge code base and I recently made a change where I changed the type of a parameter from String to a custom class. On the next compile I got all the areas where the impact was, but areas where the input type was of type Object failed. for e.g.
String str = "32"
int i = Convert.ToInt32(str)
Now I have changed String to a new custom type lets say MyCustomClass I would now want following code to fail on next compile
MyCustomClass str = new MyCustomClass("32")
int i = Convert.ToInt32(str)
but it won't as Convert.ToInt32 also accepts type Object. Is there some way I can make a change in MyCustomClass that it's not considered Object anymore.
Please note: Convert.ToInt32 is only used for sample I have many more such functions, so please focus your suggestion/answer to question asked.
Override ToString() and IConvertible
You said in the comments that your intentions are to find places where your object, which had previously been treated as a string, and are now being treated as an object.
In these situations typically, the third-party code would call .ToString() on your object to get something which it can use.
So, Convert.ToInt32(str) is equivalent to Convert.ToInt32(str.ToString()).
If you implement ToString() and IConvertible to return whatever your old version of str looked like then it should continue to work in the same way as the old version.
Probably.
Sorry I know that is not the 100% perfect compile time answer you were looking for, but I think you also know very well that your MyCustomClass will always be considered object.
Possible compile time answer:
Write a tool which uses reflection to iterate over every class/struct/interface in every system/third-party DLL.
Output a load of CS files which contain all these same classes, but just throw NotImplementedException.
(T4 could help you do this)
Compile these classes into dummy.dll
Your .csproj now references only this one dummy.dll, instead of the real dlls.
Your project should compile fine against the dummy dll.
Look at your dummy.cs files and delete any use of object.
Re-compile... and suddenly you get a load of compile time errors showing you anywhere you are using an object.
Impliment an implicit cast from MyCustomClass to String.
public static implicit operator string(MyCustomClass str)
{
return "Legacy respresentation of str";
}
This allows the complier the choice of choosing ToInt32(Object) or ToInt32(String), and I bet it favours the later.
This way all your existing function calls will remain the same so you wont have to be concerned about third party implentation details.
(Sorry, I am not at a computer right now so I can`t test that my assumtion is correct. If you do test this, be sure to consider extension methods, as they can affect the conpilers desision making in unexpected ways)
Related
I am working on a c# library, so we are concerned with breaking backwards compatibility, but I was wondering is it possible to change just the name of a parameter and maintain backwards compatibility because of the ability to use named parameters? An example of what I am trying to do is below
[Obsolete("use ChangeSpecificFoo(SpecificFoo specificFoo)")]
public void ChangeSpecificFoo(SpecificFoo foo)
{
_specificFoo = foo;
}
//Compile error ... already defines a member called 'ChangeSpecificFoo' with the same parameter types
public void ChangeSpecificFoo(SpecificFoo specificFoo)
{
_specificFoo = specificFoo;
}
Just changing the parameter name runs the potential risk of breaking backwards compatibility because someone could be calling the method using named parameters like ChangeSpecificFoo(foo: someSpecificFoo) , but we can't deprecate the method by adding a new method with the correct parameter name because parameter names are not included in the method signature, so the compiler sees it as a duplicate.
Is there any way around this? The only alternatives I see are changing the method name so it is not a duplicate and then deprecating the old method, or waiting until we add or remove parameters from the parameter list and changing the parameter names then(this may never happen because the method is pretty stable), or just make the change and fix any breaks that we may have from code using this library as we find them.
My first inclination for this is simple: DON'T. The name of your parameter is irrelevant outside of the method body. You're right to consider people calling it out by name, and therefore potentially breaking it. However, just changing the name of the parameter gives no real benefit.
The only possible reason for changing the name is to redefine what the method does because the old name leads to confusion. In that case, the name of the method should also be changed in order to not introduce another form of confusion. (The fact that the method signatures are identical is the first and more important reason to not change parameter names. However, this is to potentially explain why you might want to.)
If however, you are still adamant about keeping the same method signature, but altering the name, you could do this. (Again, I'm strongly recommending you either don't change it at all, or rename the method as well to continue to eliminate confusion.)
One way around this would be to have the method with both parameters, but make the second optional. Have that last parameter use the old name, and then assign it over within the method.
I would also HIGHLY recommend logging any uses of the named parameter, to see if your concern is valid about people calling it as a named parameter.
public void ChangeSpecificFoo(SpecificFoo specificFoo = null, SpecificFoo foo = null)
{
if (foo != null && specificFoo == null)
{
// Add any other details you can, especially
// to figure out who is calling this.
Log("Someone used a name parameter!!");
}
_specificFoo = specificFoo ?? foo;
}
As Dmitry Bychenko pointed out in the comments, this will not stop anyone from calling this method like so: ChangeSpecificFoo(null, new SpecificFoo()), which will trigger a logging.
His observation introduces another reason why this is a bad idea: You're now introducing ANOTHER way for people to "incorrectly" call your method. Therefore, I'll repeat my advice from the top of my answer: DON'T do this, unless you really really really need to change that parameter name.
I'm fairly new to C# but i'm looking to convert an object to an array of unsigned shorts. The original data is an array of WORD's (numerical value WORD) passed as an object. I've attempted the following but keep getting an error.
object temp = Agent.Port("PumpPressure1_01").Value;
ushort[] PP1_01 = ((IEnumerable)temp).Cast<object>()
.Select(x => x == null ? x.ToUshort())
.ToArray();
When I run this I get the following error:
'System.Collections.Generic.IEnumerable<T>' requires '1' type arguments.
The namespaces I used when I get the above error are:
using System.Linq;
using System.Text; // Don't think this is required but added it in case
If I add the following namespaces:
using System.Collections;
using System.Collections.Generic;
I get the following error.
'System.Linq.ParalleIEnumerable.Select<TTSource,TResult>()' is not supported by the language
I'm sure this is an obvious issue but I've been hunting the net for a while and can't find a solution. My best guess is that the Select function isn't correct as this was originally designed to convert an object to an array of strings.
Any help would be great.
Thanks
IEnumerable is a generic interface, so you have to declare the datatype you are using...
To be honest though, I would want to check what that call to
object temp = Agent.Port("PumpPressure1_01").Value;
is actually returning - by inspecting it in the debugger... If it is simply returning a reference to an array of a numeric type, you should be able to simply cast it. What you are doing though is trying to cast each individual item within the array - I suspect that's not what you should be doing - which would be casting the array itself.
Can you give us any API documentation for the Port method on the Agent object so I can see what it is meant to return? Can you try the inspection and see what that gives you?
Why you casting to IEnumerable and then casting it back to object if your temp variable is already of type object?
Also IEnumerable<T> is a generic interface and must specify exact type (as exception also says to you). If you have an array of integers and you want to work with them it should be IEnumerable<int>
Thanks for all the help and feedback.
Unfortunately I was't paying enough attention to the warnings that was posted which seems to be causing the issue.
Warning: Reference to type 'System.Func '2' claims it is defined in 'c:\Windows\Microsoft.NET\Framework64\v2.0.50727mscorlib.dll'. but it could not be found
It seems that there is some issue with the .NET reference. I have another VM which I tested the following solution on and it seemed to work without issue. Looks like I'll have to reinstall the software package to get it to work on the VM i want to use.
The software package I'm using is a custom package that uses C# to build solutions with prebuilt classes made to look like plug and play blocks. You can connect the blocks together drawings lines from one input/output of a block to another. You can then build C# code inside the blocks. Basically c# for dummy's like me..
Example of the blocks:
As for the code, I did have to make some changes as follows but now works a treat. Agent.Port("PumpPressure1_01").Value.RawValue is used to reference the particular ports on the block.
object temp = (object)Agent.Port("PumpPressure1_01").Value.RawValue;
UInt16[] PP1_01 = ((System.Collections.IEnumerable)temp).Cast<object>()
.Select(x => Convert.ToUInt16(x))
.ToArray();
foreach(UInt16 x in PP1_01)
{
Agent.LogDebug("values: " + x.ToString());
}
Again, thanks for all the help. Just need to resolve the issue with the library reference now.
I am attempting to create a function where the return type is determined at run-time. I know I could just return an object or dynamic, however my aim is to have the typed object returned, and be recognized by the compiler and InteliSense.
I know I could cast my object after it has been returned and that would be the easiest thing to do to implement this, but that is just not the programming spirit.
Here is an example of what I'm trying to create
Note: I do not actually want Buttons and Grids... that is just for this example.
Type T;
public T Question(bool aBool)
{
if (aBool)
{
T = typeof(Button);
return new Button();
}
else
{
T = typeof(Grid);
return new Grid();
}
}
Now, this obviously doesn't work and I understand why. But I want to know if anyone has a way that does work, or if this is not possible with the current state of C#.
Edit: A response to comments... I understand this would seem like "magic", and I do understand that the compiler will have to figure out what my result is for this to work. The compiler/Intellisense/Visual Studio already does this for many other things. While these things are can simple like detecting unreachable code, or drawing visual previews. I am curious if this is an implemented feature.
The only possible way for the consumer of such a method to actually rely on the fact that the return type is dynamic is if, at least for that one method call, the return type is statically known at compile time.
There is a specific feature for a method that has some type unknown at the time the method is written, but fixed when a particular call to that method is make. That feature is called "generics".
public T Foo<T>()
where T : new()
{
return new T();
}
That's really the only available option for a truly dynamic return type that has much potential for really being useful.
If that's not what you want, or that is not a workable option for you, then odds are pretty high your method shouldn't have a dynamically changing return type. Instead it should have a fixed return type of some more generalized type that can have multiple implementations. Generally this would mean an interface, to which you can return one of any number of possible implementations. This should be done if the caller doesn't need to really know or care what the implementation is, but rather all they need to know is that they are given some implementation of an interface that exposes all of what they need. In your case, perhaps something like Control would be workable, if the caller only need to know that they are given some type of control, and to which the API of Control provides everything that they need to do with it.
You can use Dynamic keyword in this case
eg:
public dynamic CreatObj(string caller)
{
if (caller.equals("x"))
return x;
else
return y;
}
You can use a type if it has a parameterless constructor and you mark your generic with the new constraint. If you want to do more than that it get more difficult you need to use refection or activator.
Note: I already checked msdn, it doesn't address my actual question, see below.
I'm trying to use the obsolete attribute on a (obviously obsolete) constructor in one of my classes. Here's the scenario:
I want to be able to force the developer to update to the new constructor without affecting already existing and deployed code. This way I can deploy my code to production just fine, but from a developers perspective, whenever they go into their code, instead of just getting a "warning" which I'm sure they'll just ignore, I want them to get a compile error because the status quo is no longer ok.
So my question is, will this affect only developers, or all calling apps, or do I have the whole thing wrong?
sample code:
public class MyClass
{
private string _userID; //new code
[Obsolete("This constructor is obsolete, please use other constructor.", true)]
public MyClass()
{
_userID = ""; //defaulting to empty string for all those using this constructor
}
public MyClass(string userID)
{
_userID = userID; //this is why they need to use this constructor
}
}
Any and all help will be appreciated, thanks in advance!
Yes, this primarily affects the compiler - any pre-built code won't be affected... unless that code explicitly checks for this attribute. For example, some serialization code (XmlSerializer, IIRC) checks for this - so it might not be entirely side-effect free... but in principal existing code won't usually be affected until they try to compile next.
Of course, if you are using this code from something that uses dynamic compilation (for example ASP.NET without pre-compile) then all bets are off.
The attribute is only an instruction to the compiler. Already existing binaries can still use the constructor.
So my question is, will this affect only developers, or all calling apps, or do I have the whole thing wrong?
This will only be used at compile time, by the compiler. It will not affect applications which have already been deployed.
As such, this will have the behavior you are trying to accomplish.
This is what [Obsolete] already does, no extra help is needed. It is not a compile time warning, it generates an error:
error CS0619: 'ConsoleApplication1.MyClass.MyClass()' is obsolete:
'This constructor is obsolete, please use other constructor.'
I have inherited a small scripting language and I am attempting to port it to the DLR so that it is a little easier to manage. So far it has been fairly straight forward. I have run into a problem though attempting to dynamically call members of a variable. The current language runs on .NET and uses a parsing loop and reflection to do this, but I was hoping to get away from that. Here is an example of the script language:
string $system1RemoteUri;
string $dbconnection = $config.GetDBConnection ("somedb");
float $minBad = 0.998;
float $minGood = 0.2;
$systen1RemoteURI, $minBad, and $minGood are variables that will be set in the script, along with $dbconnection. However $dbconnection will get its value from a variable passed in called $config. The 4 variables need to be available to the caller, so they are passed into the lambda, initially as null. Here is the generated Lambda IL (debug view):
.Lambda #Lambda1<Delegate6$1>(
System.String& $$system1RemoteUri,
System.String& $$dbconnection,
System.Double& $$minBad,
System.Double& $$minGood
System.Object $$config) {
.Block() {
$$minBad = 0.998D;
$$minGood = 0.2D
}
//Some assignment similar to...
//.Dynamic Call GetDBConnection($config, "somedb");
}
What I am trying to figure out is how to use Expression.Dynamic to emit the $config.GetDBConnection("somedb"). From looking at examples in the Sympl libraries I believe the emitted IL should look like:
.Dynamic Call GetdbConnection($config, "somedb") but I cant figure out how to actually emit that from Expression.Dynamic.
It seems to want a CallSiteBinder which I cannot create correctly, and I do not understand what the order of parameters is to Expression.Dynamic, as it seems to only want the "member" being invoked, and not the base.
I do not know the runtime type of $config it is just some object which implements a function called GetDBConnection(string). This is not provided by an interface or base class.
Any help would be appreciated.
You can either turn this into an InvokeMemberBinder or turn "$config.GetDBConnection" into a GetMember and then do an Invoke on the result of that passing $someDb as the argument.
To implement your GetMemberBinder and InvokeMemberBinder you can use the DLR outer-layer DefaultBinder class. In the latest IronPython/IronRuby source code you can just create a new DefaultBinder instance out of thin air. Then in your FallbackGetMember / FallbackInvoke you can call defaultBinder.GetMember(...) and defaultBinder.Call (which should be renamed Invoke). That'll deal with most .NET types for you. Also all objects which implement IDynamicMetaObjectProvider will work with it as well. For other dynamic operations you can use the other methods on the default binder. And if you want to start customizing your overload resolution and binding rules it has lots of knobs you can turn.
Unfortunately the default binder doesn't have an InvokeMemberBinder implementation right now so you're probably better off w/ GetMember/Invoke.