right now iam trying to create some Stored Procedures for a HSQL-DB.
I want to create a new User and return the ID of the new User.
For example i tried it like this to create the Procedure.
create procedure test(out param int)
modifies sql data
begin atomic
set param = 1;
end;
=> Call it
declare param int ;
call test(param);
call param;
=> Error
dynamic parameter or variable required as INOUT or OUT argument
I can´t find the bug -.-
so long.
This is how you call the procedure:
declare param int;
call test(param)
call param
It looks the same, but each statement is executed separately!
Related
I'm trying to overwrite an array inside a method. The compiler is giving me the error "Error: LHS of assignment must denote a mutable variable".
method invalidSort(a : array<int>)
modifies a;
requires a != null;
ensures sorted(a[..]);
{
a := new int[0];
}
Am I staring myself blind and missing something or why does Dafny not allow this?
In Dafny, method parameters cannot be assigned to. You can use a local variable if you need to update the value internally.
For example,
var a' := new int[0];
If you want this new array to be available to the caller, you'll also need to return it.
return a';
All that said, if you're trying to write an in-place sorting method, then you don't need to do any of this. Just modify a in place.
a[0] := 0;
// ...
In the same way we can have
nullableClassInstance?.method(blah)
Is there a way to do
nullableFunctionInstance?(blah)
In other words, is there an operator that checks whether a function instance is not null, if so, invoke the function all in one line?
Using the call method, you can achieve what you want with:
nullableFunctionInstance?.call(blah)
There's also the apply method if you want to pass arguments.
If you have a Function Object , you can use the call method and send all the parameters to that which works exactly as calling the function. Here , you can use the null aware member access operator.
void myFun(int a , int b){...}
var myVar = myFun ;
call
The function myVar will only get called if its not null as shown below.
myVar?.call( arg1 , arg2 );
apply
If your function is dynamic or you wish to control which function is being called at run time , you can use the apply static method of Function like so :
Function.apply(myVar , [arg1 , arg2]);
apply takes the function and a List of parameters that will be sent to the function.
Read more about call and apply :
I'm making a function in Delphi that needs a specific value as parameter, unless it is set when function is called. While te default parameter be overwritten in that case?
example:
function ExampleFunction(b = 3, a){
b*a = c
}
ExampleFunction(15,2)
Will the default parameter(3) be replaced with the given parameter(15)?
Your code does not compile. Its syntax is invalid. It looks rather as though you have written the code in some hybrid of Pascal and C#. I suggest that you fix the question.
What's more, default parameters must appear last in the list. The reason for that is that default parameters allow you to omit an parameter when calling the function. When you do that, the compiler substitutes the missing parameter with the default value. Because parameters are positional, it is not possible to omit a parameter, but then pass another parameter that appears after it in the list.
The documentation, which I urge you to read one more time, says:
Parameters with default values must occur at the end of the parameter list. That is, all parameters following the first declared default value must also have default values.
Now to the question. If you do not omit the parameter, that is if you provide it, then the value you provided is used.
Let's use an example that actually compiles:
function Test(a: Integer; b: Integer = 42): Integer;
begin
Result := a * b;
end;
Then
Test(2) = 84 // parameter b is omitted, default value passed
and
Test(4, 3) = 12
In Delphi, suppose I have a method with a (much simplified) signature like this:
procedure abc( const prop1:string; const arg1:TValue; const prop2:string;
out arg2:TValue );
I'm building a TList<PPropValPair> of records like this using the parameters provided:
type
TPVPType = (ptIn, ptOut);
PPropValPair = ^TPropValPair;
TPropValPair = record
io : TPVPType;
prop : string; // property name
iVal : TValue; // input value
oVar : Variant; // <-- how to save for later use??? Variant? TValue?
end;
(On the face of it, this example looks silly. Again, it's quite simplified just to communicate the problem.)
At run-time, I want to stuff all of the input values ival (where io=ptIn) into each public property 'prop' in a class, call a class method, then extract the values of all public properites 'prop' (where io=ptOut) into oVar.
The input side is working fine using RTTI.
However, I need to somehow save a REFERENCE to the output vars in oVar so I can save the value of the associated properties after the class method has been called.
I'm not assigning anything to arg2 directly. Rather, I'm saving a reference to arg2 and assigning the value indirectly later on.
The trick is ... I don't want to have to do any additional annotations of the output parameters in abc(...).
In C++, you can declare a parameter as a 'reference' by prepending it with '&'. So in C++ terms this might be defined roughly as:
procedure abc( arg1 : TValue; &arg2 : TValue );
Later, you can refer to &arg2 and it's using a POINTER to the object. But in calling the function, you just say:
abc( somevar1, somevar2 );
somevar1 is passed by value, and somevar2 is passed by reference. Inside the function, I can save somevar2 in a reference var, then later on assign a value to it via the pointer (if it's a string) by saying &arg2ref = 'abc'.
I'm guessing there's a way to do this in Delphi, either with a Variant as the oVar type, or using RTTI, or something else. I just haven't figured out the magic combination of pieces yet. (I just don't use pointers very often in Delphi.)
Maybe I need to save a raw pointer in oVar along with the type (say, oType), and cast a value through the pointer to save the property's value?
I'm hoping someone here might have some clear ideas.
BTW, I'm using Delphi XE3.
Use a pointer. It doesn't have to (and indeed shouldn't) be a "raw" pointer. Use a typed pointer, PValue. Pass in a PValue to your function, and then store that in oVal, which you should also declare a a PValue. Use # to create a pointer, and ^ to dereference.
I would not recommend passing arg2 by reference. Although you can still use # on it to get a pointer to the original variable passed to abc, the reference parameter disguises the fact that the variable needs to remain available indefinitely. Instead, declare arg2 as PValue so it's more obvious to the caller that indirection is involved.
// declaration
procedure abc(...; arg2: PValue);
// call
abc(..., #somevar2);
How do I execute a SP and get the return value. The below code always returns null object. The storedprocedure has been tested in the database using the same parameters as in code, but the SubSonic sp always returns null. When executed in the db via sql, it returns the correct values.
This is using SubSonic 3.0.0.3.
myDB db = new myDB();
StoredProcedure sp = db.GetReturnValue(myParameterValue);
sp.Execute();
int? myReturnValue = (int?)sp.Output;
In the above code, sp.Output is always null. When executed in the database, the returned variable is a valid integer (0 or higher) and is never null.
Stored procedure code below:
CREATE PROCEDURE [dbo].[GetReturnValue]
#myVariable varchar(50)
AS
declare #myReturn int
BEGIN
set #myReturn = 5;
return #myReturn;
END
When executing the stored proc in SQL Server, the returned value is '5'.
I copied your sproc and stepped through the SubSonic code and .Output is never set anywhere. A work around would be using an output parameter and referring to it after executing: sproc.OutputValues[0];
Here's a simple way to do it:
In the stored procedure, instead of using RETURN, use SELECT like this:
SELECT ##ROWCOUNT
or
SELECT #TheIntegerIWantToReturn
Then in the code use:
StoredProcName.ExecuteScalar()
This will return the single integer you SELECTED in your stored procedure.
CREATE PROCEDURE [dbo].[GetReturnValue]
#myVariable varchar(50)
#myReturn BIGINT OUTPUT
AS
declare #myReturn int
BEGIN
set #myReturn = 5;
return #myReturn;
END