I'm trying to create this sort of Map:
var map:Map = new Map<Dynamic, Array<ProductData>>();
But compiler throws an error : Unexpected ;
So it doesn't like the types declaration nesting. But I really do need that Array<ProductData> as a value of a map.
How can I overcome this mistake?
That's interesting, since I get a different error with that code:
Invalid number of type parameters for Map
That is fixed by removing the :Map though (just let type inference handle that).
After that, though, I get the following error:
Abstract Map has no #:to function that accepts IMap>
...or in other words - you can't have a Map with Dynamic keys in Haxe. Why are you using Dynamic there in the first place? Could that maybe be statically typed?
Related
Try to make as described:
To convert a string to lowercase, you can call the String.ToLower()
method
let makeUpperCase s =
s.ToUpper()
Get as result
error FS0072: Lookup on object of indeterminate type based on
information prior to this program point. A type annotation may be
needed prior to this program point to constrain the type of the
object. This may allow the lookup to be resolved.
If you want to invoke members of a value that is passed as an argument to a function, you have to give F# some hint about what the type of the value is. The best way to do this is using a type annotation:
let makeUpperCase (s:string) =
s.ToUpper()
F# compiler needs this, because it cannot figure out what ToUpper method are you trying to invoke as there may be many .NET objects that have a method of this name.
First, let me say that I agree that eval(repr(some_string)) is potentially a bad idea. But it is a thing that exists, and I have a specific question about it.
Why doesn't this work?
my_type = int
my_type_str = repr(int)
my_type_from_str = eval(my_type_str)
To clarify, I know specifically why the eval call fails. The command repr(int) produces a string which cannot be automatically interpreted. I guess my issue is that this isn't behaving as I expect... so either my expectation is faulty or the implementation is faulty. Which is it?
Side Note
There are some tricks that can be used to get around this default behavior, some obvious, some not. For instance, this:
my_type = int
my_type_str = my_type.__name__
my_type_from_str = eval(my_type_str)
assert my_type is my_type_from_str
This sets off my "hack" alert hardcore, and I don't like it (or other similar hacks, for instance parsing the string "<class 'int'>" with some home made function).
The documentation explains:
Return a string containing a printable representation of an object. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval(), otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a repr() method.
(emphasis mine)
So, it doesn't say that repr must always return valid Python code - sometimes it's not the case. Just another argument for not relying on it.
I am very new to Xtext/Xtend, therefore apologies in advance if the answer is obvious.
I would like to allow the end-users of my DSL to define a 'filter', that when applied and 'returns' true it means that they want to 'filter out' the given entity of data from consideration.
I want to allow them 2 ways of defining the filter
A) by introspecting the attributes of a given data object and apply basic rules like
if (obj.field1<CURRENT_DATE && obj.field2=="EXPIRED)
{ return true;} else {return false;}
B) by executing a controlled snippet using 'eval' of my host language
In other words, the user would be expected to type into a string/code block a valid
code snippet of the hosting language
I had decided that the easiest way for me support case A) would be to leverage the XBase rules (including expressions/etc)
Therefore I defined filters (mostly copying the ideas from Lorenzo's book)
Filter:
(FilterDSL | FilterCode);
FilterDSL:
'filterDSL' (type=JvmTypeReference)? name=ID
'(' (params+=FullJvmFormalParameter (',' params+=FullJvmFormalParameter)*)? ')'
body=XBlockExpression ;
FilterCode:
'filterCode' (type=JvmTypeReference)? name=ID
'(' (params+=FullJvmFormalParameter (',' params+=FullJvmFormalParameter)*)? ')'
'{'
body=STRING
'}';
Now when trying to implement the Java mapping for my DSL, via the inferrer stub in Xtend -- I am running into multiple problems.
All of them likely indicate that I am missing some fundamental understanding
Problem 1) fl.body is not defined. fl Is of type Filter, not FilterDSL or FilterCode
And I do not understand how to check what type a given instance is of, so that I can access the content of a 'body' feature.
Problem 2) I do not understand where 'body' attribute in the inferrer method is defined and why. Is this part of ECore? (I could not find it)
Problem 3) what's the proper way to allow a user to specify a code block? String seems to be not the right thing as it does not allow multiline
Problem 4) How do I correctly convert a code block into something that is accepted by the 'body' such that it ends up in the generated code.
Problem 5) How do I setup multiple inferrers (as I have more than one thing for which I need the code generated (mostly) by xBase code generator)
Appreciate in advance any suggestions, or pointer to code examples solving similar problems.
As a side observation, Inferrer and its interplay with XBase has sofar been the most confusing and difficult thing to understand.
in general: have a look at the xtend docs at xtend-lang.org
You can do a if (x instanceof Type) or a switch statement with Type guards (see domain model example)
i dont get that question. both your FilterDSL and FilterCode EClasses should have a field+getter/setter named body, FilterCode of type String, FilterDSL of type XBlockExpression. The JvmTypesBuilder add extension methods to JvmOperation called setBody(String) and setBody(XExpression), syntax sugar lets you call body = .... instead of setBody(...)
(btw you can do crtl+click to find out where a thing is defined)
strings are actually multiline
is answered by (2)
you dont need multiple inferrers, you can infer multiple stuff e.g. by calling toClass or toField multiple times for the same input
This is what I am trying to do:
public void method(int myVal, string myOtherVal)
{
// doing something
}
dynamic myVar = new SomeDynamicObjectImplementer();
method(myVar.IntProperty, myVar.StringProperty);
Note that my properties are also DynamicObjects. My problem is that the TryConvert method is never called and that I get a runtime error saying the method signature is invalid.
The following is working great:
string strVar = myVar.StringProperty;
int intVar = myVar.IntProperty;
And I would like to avoid
method((int)myVar.IntProperty, (string)myVar.StringProperty);
Is it possible to override something in DynamicObject to allow this? (or something else)
Thank you
The problem is your assumption that it will try a dynamic implicit convert on arguments of an dynamic invocation to make a method call work, this is not true.
When your arguments aren't statically typed, it will use the runtime type to find the best matching method (if the runtime type matches the static rules for implicit conversion to the argument type this will work too), since your your IntProperty,StringProperty seem to be returning a DynamicObject rather than an Int and a String or something that could statically be converter implicitly, this lookup will fail.
If SomeDynamicObjectImplementer could actually return an Int for IntProperty and a String for StringProperty your method call for without casting would actually work. It's also probably a better dynamic typing practice if you data type is based on the actually type of data rather than usage using try convert. You could add actually implicit convert methods for every possible type that you could return to that returned DynamicObject type, but that could cause strange resolution issues to depending on how much you are overloading.
However, another option to keep your dynamic implementation the same is to mix a little controlled static typing in, you can use ImpromputInterface (in nuget) to put an interface on top of a dynamic object, if you do that then the TryConvert method would be called on your returned DynamicObjects.
public interface ISomeStaticInterface{
int IntProperty {get;}
string StringProperty {get;}
}
...
var myVar = new SomeDynamicObjectImplementer().ActLike<ISomeStaticInterface>();
method(myVar.IntProperty, myVar.StringProperty);
Instead of using myVar.IntProperty can't you just put them in variables first, like you already did, and then use then for your method?
so method(intVar , strVar); seems fine. At least more elegant than casting.
Of course, if you're already certain your object will have IntProperty and StringProperty, why not just make an actual object with those properties instead?
Why are you doing the cast?
method(myVar.IntProperty, myVar.StringProperty);
should compile.
If the two properties must be the types suggested by the names then they shouldn't be dynamic.
I'm getting an error while trying to load an record through the constructor.
The constructor is:
public Document(Expression<Func<Document,bool>> expression);
and i try to load a single item in like this
var x = new Document(f=>f.publicationnumber=="xxx");
publicationnumber isn't a key but tried making an it an unique key and still no go..
Am i totally wrong regarding the use of the constructor? and can someone please tell me how to use that constructor?
The error i'm getting is:
Test method TestProject1.UnitTest1.ParseFileNameTwoProductSingleLanguage threw exception: System.NullReferenceException:
with the following stacktrace:
SubSonic.Query.SqlQuery.Where[T](Expression1` expression)
Load`[T]`(T item, Expression1expression)
db.Document..ctor(Expression``1 expression) in C:\#Projects\DocumentsSearchAndAdmin\DocumentsSearchAndAdmin\Generated\ActiveRecord.cs: line 5613
rest removed for simplicity
Regards
Dennis
Use == instead of =, i.e.:
...(f=>f.publicationnumber == "xxx");
I've just gotten the SubSonic source, and found out that it had to with the expression parser and my lack of knowledge thereof .. my right side of the expression was actually an item in an string array - and s[PUBNO] (PUBNO is a const) and it was looking for an column named s instead of publicationnumber, i don't know if this i a bug or not in the linq classes
none the less - i've managed to get it to work by creating a local variable containing the value of s[PUBNO] and using that instead...
//dennis