int sum= value.stream().reduce(0,(ans,i)-> ans +i);
The method reduce(integer, BinaryOperators Integer>) from the type Stream refers to the missing type BinaryOperator
The target type of this expression must be a functional interface
I tried creating parameters
Related
I'm fairly new to Kotlin. I want to print the count of a character in a string. For this, I'm using Kotlin's groupingBy() function and applying eachCount() to it.
My code:
val str = "0100101101010"
val countMap : Map<Char, Int> = str.groupingBy { it }.eachCount()
println(countMap["1"])
But I'm getting this error in the console: Type inference failed. The value of the type parameter K should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.
Can someone explain to me what I'm doing wrong here?
"1" is a string literal, but your map has characters as keys. You should use the character literal '1':
println(countMap['1'])
The reason for that confusing error message is because it is trying to call this get overload, which is generic. It tries to infer the generic type arguments, and fails.
I want to deal with a structure like this struct foo {char *name; char **fields ; size_t nfields};
If I define corresponding structure in Squeak
ExternalStructure subclass: #Foo
instanceVariableNames: ''
classVariableNames: ''
poolDictionaries: ''
category: 'FFI-Tests'.
and define the fields naively with
Foo class>fields
^#(
(name 'char*')
(fields 'char**')
(nfields 'unsigned long')
)
then generate the accessors with Foo defineFields, I get those undifferentiated types for name and fields:
Foo>>name
^ExternalData fromHandle: (handle pointerAt: 1) type: ExternalType char asPointerType
Foo>>fields
^ExternalData fromHandle: (handle pointerAt: 5) type: ExternalType char asPointerType
That is troubling, the second indirection is missing for the fields accessor.
How should I specify fields accessor in the spec?
If not possible, how do I define it manually?
And I have the same problem for this HDF5 function prototype: int H5Tget_array_dims(hid_t tid, hsize_t *dims[])
The following syntax is not accepted:
H5Tget_array_dims: tid with: dims
<cdecl: long 'H5Tget_array_dims'(Hid_t Hsize_t * * )>
The compiler barks argument expected -> before the second *...
I add to resort to void * instead, that is totally bypassing typechecking - less than ideal...
Any idea how to deal correctly with such prototype?
Since Compiler-mt.435, the parser will not complain anymore but call back to ExternalType>>asPointerToPointerType. See source.squeak.org/trunk/Compiler-mt.435.diff and source.squeak.org/FFI/FFI-Kernel-mt.96.diff
At the time of writing this, such pointer-to-pointer type will be treated as regular pointer type. So, you loose the information that the external type actually points to an array of pointers.
When would one need that information?
When coercing arguments in the FFI plugin during the call
When constructing the returned object in the FFI plugin during the call
When interpreting instances of ExternalData from struct fields and FFI call return values
In tools such as the object explorer
There already several kinds of RawBitsArray in Squeak. Adding String and ExternalStructure (incl. packed or union) to the mix, we have all kinds of objects in Squeak to map the inner-most dimension (i.e., int*, char*, void*). ExternalData can represent the other levels of the multi-dimensional array (i.e., int**, char**, void** and so on).
So, there are remaining tasks here:
Store that pointer dimension information maybe in a new external type to be found via ExternalType>>referencedType. We may want to put new information into compiledSpec. See http://forum.world.st/FFI-Plugin-Question-about-multi-dimensional-arrays-e-g-char-int-void-td5118484.html
Update value reading in ExternalArray to unwrap one pointer after the other; and let the code generator for struct-field accessors generate code in a similar fashion.
Extend argument coercing in the plugin to accept arrays of the already supported arrays (i.e. String etc.)
I'm using reflection to serialize an object. Getting the values as objects is a real murder on performance due to late binding penalties. CType / DirectCast can get rid of most of it but I can't feed a type variable into it so currently I'm using a switch case block on the type variable to select the correct DirectCast.
It came to my attention that CTypeDynamic exists and takes type variables but the return type is Object so... it converts an object into an object, cool. That got me wondering, what is the purpose of this function?
The CTypeDynamic function looks for dynamic information and performs the cast/conversion appropriately. This is different from the CType operator which looks for static information at compile time or relies on the types being IConvertible.
This function examines the object at runtime including looking for Shared (aka static) custom operators. As always, if you know the type then use CType, but if you need dynamic casting then you need to use CTypeDynamic.
More information here: http://blogs.msmvps.com/bill/2010/01/24/ctypedynamic/
Can I define an ABAP method where the RETURNING parameter and any IMPORTING parameters have a generic type but that can still be called in a single line as a functional method?
In other words I'd like to replace this:
CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'
EXPORTING
input = lv_external_value
IMPORTING
output = lv_internal_value.
With:
lv_internal_value= zcl_conversion=>alpha_input( lv_external_value ).
Unfortunately the fact that Class Methods can't have an untyped returning parameter is preventing me from declaring the functional method's return value as type ANY or CLIKE. The accepted standard of creating generic method parameters seems to be to define them as TYPE REF TO DATA and dereference/assign them. But as far as I know that prevents me from calling the method in a single statement as I have to first assign the importing parameter and then dereference the returning parameter, resulting in the same or more lines of code than a simple FM call.
Is there a way around this?
Unfortunately, there is no other way to dereference data than to use the dereference operator, either in the form ->* for the full value segment, or in the form ->comp, if the data object is structured and has a component named comp (and, even worse, there are a lot of places in ABAP code where you would like to use a value from a derefenced data object but can't do it for internal reasons / syntax restrictions).
However, you could simply keep the data reference object retrieved by your method in a variable of the calling code and work with that variable (instead of using a field symbol or a variable for the derefenced value segment itself). Either generically, as a ref to data variable, or typed, using the CAST operator (new ABAP syntax).
Most things that can be done with a field-symbol, can also be done directly with a data reference as well.
Example: Working with a variable result of the expected return type:
data(result) = cast t000( cl=>m( ) ).
write result->mandt.
See here the full example:
report zz_new_syntax.
class cl definition.
public section.
class-methods m returning value(s) type ref to data.
endclass.
start-of-selection.
data(result) = cast t000( cl=>m( ) ).
write: / result->mandt. " Writes '123'.
class cl implementation.
method m.
s = new t000( mandt = '123' ).
endmethod.
endclass.
On ABAP NW Stack 7.4 you could just use parameters type STRING and then use the new CONV Operator to convert your actual input in string. Little ugly but should work.
lv_internal_value = CONV #(zcl_conversion=>alpha_input( CONV #(lv_external_value) )).
I'm trying register presenters with Windsor using the convention based method but trying to do this in VB.NET, but the problem is it does not want to compile this statement:
Dim type = GetType(AbstractPresenter(Of))
I am getting : Too few type arguments to AbstractPresenter(Of TView, TPresenter)
Which I don't understand because this is a valid statement according to question. Also showing valid in other C# to VB.NET converters when converting typeof(AbstractPresenter<>).
Any ideas?
There are two type arguments, and you need to specify this, just as you would do for multi-dimensional arrays:
Dim type = GetType(AbstractPresenter(Of ,))
Looks weird, but now the compiler knows that AbstractPresenter expects two type arguments.
By the way, C# has the same requirement. So the above would be written as:
var type = typeof(AbstractPresenter<,>);