Is it possible to overload methods using ExcelDNA?
For instance, my current code:
[ExcelFunction(Category = "Test",
IsVolatile=true)]
public static String TestMethod()
{
return "Hello Everyone";
}
[ExcelFunction(Category = "Test",
IsVolatile = true)]
public static String TestMethod(String Name)
{
return "Hello, " + Name;
}
It seems like it should be this straightforward, but it doesn't appear to work when you call the methods from Excel - in fact, they don't even appear (but one would appear if you commented out the other).
I don't think ExcelDna supports function overloading. I think the best way to approach your problem is to write one function that takes one object as a parameter. Then check whether the object is System.Reflection.Missing - if so it means nothing was passed.
Chris
Related
Similar questions have been asked before, such as String literal matches bool overload instead of std::string.
But what I want to know is what should C++ developers do to prevent this from happening? As someone who writes C++ libraries for others to consume, what should I do to ensure this doesn't happen? Here is the example I ran into today, where a library had 2 initialize() methods:
void initialize(bool someflag) { /* ... */ }
void initialize(const std::string & name) { /* ... */ }
Now the problematic code was in the application that wanted to utilize this functionality and which called it in a manner similar to this:
initialize("robert");
At first glance you'd think that this would call initialize(string) but it actually calls the first initialize(bool) with a boolean flag set to true!
Yes, I know it can be fixed with this:
initialize( std::string("robert") );
But this puts the onus on the caller.
Edit for #zdan: I didn't consider the "solutions" in the other linked question to be great solutions since 1) I was hoping not to have to add a const char * version of every method that takes a bool or string, and 2) the template solution increases the maintainability of the code significantly for affected methods, renders them almost unreadable.
what should I do to ensure this doesn't happen?
One possibility is to create an overload that accepts a char const* and make it a pass through to the overload that accepts a std::string.
void initialize(char const* name) { initialize(std::string(name)); }
I have a routine that does some moderately expensive operations, and the client could consume the result as either a string, integer, or a number of other data types. I have a public data type that is a wrapper around an internal data type. My public class looks something like this:
class Result {
public:
static Result compute(/* args */) {
Result result;
result.fData = new ExpensiveInternalObject(/* args */);
return result;
}
// ... constructors, destructor, assignment operators ...
std::string toString() const { return fData->toString(); }
int32_t toInteger() const { return fData->toInteger(); }
double toDouble() const { return fData->toDouble(); }
private:
ExpensiveInternalObject* fData;
}
If you want the string, you can use it like this:
// Example A
std::string resultString = Result::compute(/*...*/).toString();
If you want more than one of the return types, you do it like this:
// Example B
Result result = Result::compute(/*...*/);
std::string resultString = result.toString();
int32_t resultInteger = result.toInteger();
Everything works.
However, I want to modify this class such that there is no need to allocate memory on the heap if the user needs only one of the result types. For example, I want Example A to essentially do the equivalent of,
auto result = ExpensiveInternalObject(/* args */);
std::string resultString = result.toString();
I've thought about structuring the code such that the args are saved into the instance of Result, make the ExpensiveInternalObject not be calculated until the terminal functions (toString/toInteger/toDouble), and overload the terminal functions with rvalue reference qualifiers, like this:
class Result {
// ...
std::string toString() const & {
if (fData == nullptr) {
const_cast<Result*>(this)->fData = new ExpensiveInternalObject(/*...*/);
}
return fData->toString();
}
std::string toString() && {
auto result = ExpensiveInternalObject(/*...*/);
return result.toString();
}
// ...
}
Although this avoids the heap allocation for the Example A call site, the problem with this approach is that you have to start thinking about thread safety issues. You'd probably want to make fData an std::atomic, which adds overhead to the Example B call site.
Another option would be to make two versions of compute() under different names, one for the Example A use case and one for the Example B use case, but this isn't very friendly to the user of the API, because now they have to study which version of the method to use, and they will get poor performance if they choose the wrong one.
I can't make ExpensiveInternalObject a value field inside Result (as opposed to a pointer) because doing so would require exposing too many internals in the public header file.
Is there a way to make the first function, compute(), know whether its return value is going to become an rvalue reference or whether it is going to become an lvalue, and have different behavior for each case?
You can achieve the syntax you asked for using a kind of proxy object.
Instead of a Result, Result::compute could return an object that represents a promise of a Result. This Promise object could have a conversion operator that implicitly converts to a Result so that "Example B" still works as before. But the promise could also have its own toString(), toInteger(), ... member functions for "Example A":
class Result {
public:
class Promise {
private:
// args
public:
std::string toString() const {
auto result = ExpensiveInternalObject(/* args */);
return result.toString();
}
operator Result() {
Result result;
result.fData = new ExpensiveInternalObject(/* args */);
return result;
}
};
// ...
};
Live demo.
This approach has its downsides though. For example, what if, instead you wrote:
auto result = Result::compute(/*...*/);
std::string resultString = result.toString();
int32_t resultInteger = result.toInteger();
result is now not of Result type but actually a Result::Promise and you end up computing ExpensiveInternalObject twice! You can at least make this to fail to compile by adding an rvalue reference qualifier to the toString(), toInteger(), ... member functions on Result::Promise but it is not ideal.
Considering you can't overload a function by its return type, and you wanted to avoid making two different versions of compute(), the only thing I can think of is setting a flag in the copy constructor of Result. This could work with your particular example, but not in general. For example, it won't work if you're taking a reference, which you can't disallow.
In my code I have an if-else block condition like this:
public String method (Info info) {
if (info.isSomeBooleanCondition) {
return "someString";
}
else if (info.isSomeOtherCondition) {
return "someOtherString";
}
else if (info.anotherCondition) {
return "anotherStringAgain";
}
else if (lastCondition) {
return "string ...";
}
else return "lastButNotLeastString";
}
Each conditional branch returns a String.
Since if-else statements are difficult to read, test and maintain, how can I replace?
I was thinking to use Chain Of Responsability Pattern, is it right in this case?
Is there any other elegant way that I can do that?
I am left to assume that your code does not exist in the Info class as it is passed in an referenced for all but that last condition. My first instinct would be to make String OtherClass.method(Info) into String Info.method() and have it return the appropriate string.
Next, I would take a look at the conditions. Are they really conditions or can they be mapped to a table. Whenever I see code performing a lookup, such as this, I tend to fall back on attempting to fit into a dictionary or map so I can perform a lookup for the value.
If you are left with conditions that must be checked then I would begin thinking about lambdas, delegates or custom interface. A series of if..then across the same type could easily be represented. Next, you would collect them and execute accordingly. IMO, this would make the if..then bunch much clearer. It is more code by is secondary at this point.
interface IInfoCheck
{
bool TryCheck(Info info, out string);
}
public OtherClass()
{
// Setup checks
CheckerCollection.add(new IInfoCheck{
public String check(out result) {
// check code
}
});
}
public String method(Info info) {
foreach (IInfoCheck ic in CheckerCollection)
{
String result = null;
if (ic.TryCheck(out result))
{
return result;
}
}
}
The problem statement does not fit into an ideal chain of responsibility scenario because it is either/or kind or conditions which look 'chained' but is actually 'not'. Reason - one processes all the chain-links in the chain of responsibility pattern irrespective of what happened in the previous links, i.e. no chain-links are skipped(although you can configure which chain links to process and which not - but still the execution of a chain-link is not dependent on the outcome of a previous chain-link). However, in this if-else-if* scenario - once an if statement condition matches, the further conditions are not evaluated.
I have thought of an alternative design which achieves the above without if-else, but it is lengthier but at the same time more flexible.
Lets say we have a FunctionalInterface IfElseReplacer which takes 'info' as input and gives 'String' output.
public Interface IfElseReplacer(){
public String executeCondition(Info);
}
Then the above conditions can be re-phrased as lambda expressions would look like -
"(Info info) -> info.someCondition ? someString"
"(Info info) -> info.anotherCondition ? someOtherString"
and so on...
Then we need a processConditons method to process these Lambdas- it could be a default method in ifElseReplacer -
default String processConditions(List<IfElseReplacer> ifElseReplacerList, Info info){
String strToReturn="lastButNotLeastString";
for(IfElseReplacer ifElseRep:ifElseReplacerList){
strToReturn=ifElseRep.executeCondition(info);
if(!"lastButNotLeastString".equals(strToReturn)){
break;//if strToReturn's value changes i.e. executeCondition returns a String valueother than "lastButNotLeastString" then exit the for loop
}
return strToReturn;
}
What remains now is to (I am skipping the code for this - please let me know if you need it then will write this also) -
From wherever the if-else conditions need to be checked there -
Create an array of lambda expressions as explained above assigning them to IfElseReplacer interfaces while adding them to a list of type IfElseReplacer.
Pass this list to the default method processConditions() along with an instance of Info.
Default method would return the String value which we would be same as the result of if-else-if* block given in the problem statement.
I'd simply factor out the returns:
return
info.isSomeBooleanCondition ? "someString" :
info.isSomeOtherCondition ? "someOtherString" :
info.anotherCondition ? "anotherStringAgain" :
lastCondition ? "string ..." :
"lastButNotLeastString"
;
From the limited information about the problem, and the code given, it looks like this a case of type-switching. The default solution would be to use a inheritance for that:
class Info {
public abstract String method();
};
class BooleanCondition extends Info {
public String method() {
return "something";
};
class SomeOther extends Info {
public String getString() {
return "somethingElse";
};
Patterns which are interesting in this case are Decorator, Strategy and Template Method. Chain of Responsibility has another focus. Each element in the chain implement logic to process some commands. When chained, an object forwards the command if it cannot process it. This implements a loosly coupled structure to process commands where no central dispatch is needed.
If computing the string on the conditions is an operation, and from the name of the class I am guessing that it is probably an expression tree, you should look at the Visitor pattern.
I am trying to use GMock (google mocking framework for c++) for the first time. I have the following class:
class LocalCache
{
public:
virtual time_t GetCurrentTime() = 0;
virtual int AddEntry(const std::string key, std::string& value);
virtual int GetEntry(const std::string key, std::string& value);
};
The GetEntry method invokes GetCurrentTime call. I'd like to mock the GetCurrentTime method so that I can advance the clock in my test to test the aging out of entries which happens as part of the GetEntry call (please don't ask me why the aging is being done as part of GetEntry call... that's another discussion :( ). Here's my mock class:
class MockLocalCache : public LocalCache
{
public:
using LocalCache::GetCurrentTime;
MOCK_METHOD0(GetCurrentTime, time_t());
MockLocalCache()
: mCurrentTime(0)
{
}
void EnableFakeTime()
{
ON_CALL(*this, GetCurrentTime()).WillByDefault(Return(mCurrentTime));
}
void SetTime(time_t now) { mCurrentTime = now; }
private:
time_t mCurrentTime;
};
TEST(MockTest, TimeTest)
{
MockLocalCache mockCache;
mockCache.EnableFakeTime();
std::string key("mykey");
std::string value("My Value");
EXPECT_TRUE(mockCache.AddEntry(key, value));
mockCache.SetTime(10); // advance 10 seconds
std::string expected;
EXPECT_TRUE(mockCache.GetEntry(key, expected));
}
When I run the test, I expected the mCurrentTime value to be return by my mock GetCurrentTime function. However, I get the following error output:
GMOCK WARNING:
Uninteresting mock function call - taking default action specified at:
..../test_local_cache.cpp:62:
Function call: GetCurrentTime()
Returns: 0
Stack trace:
Would appreciate it if someone can let me know what I am doing wrong and how to fix it. Thanks in advance.
The solution to your problem is to make it in much simpler way. Just use EXPECT_CALLwhere you expect call to your mocked function:
class MockLocalCache : public LocalCache
{
public:
MOCK_METHOD0(GetCurrentTime, time_t());
};
TEST(MockTest, TimeTest)
{
MockLocalCache mockCache;
std::string key("mykey");
std::string value("My Value");
EXPECT_TRUE(mockCache.AddEntry(key, value));
EXPECT_CALL(mockCache, GetCurrentTime()).WillOnce(Return(10)); // advance 10 seconds
std::string expected;
EXPECT_TRUE(mockCache.GetEntry(key, expected));
}
Just to answer why your example did not work - with this call, the current value of your member variable is stored - later change to it has no effect:
ON_CALL(*this, GetCurrentTime()).WillByDefault(Return(mCurrentTime));
Look in google-mock-doc for difference between Return and Return(ByRef...
Probably - I did not check this, calling set member value, before calling setting this default would also work - but as I said - for your case EXPECT_CALL shall be used:
mockCache.SetTime(10); // advance 10 seconds
mockCache.EnableFakeTime();
Just for the record (and future people finding this question, like me), while PiotrNycz's answer is the best option when you can do it (keeping test values directly within tests) -- in some cases it really is necessary to return a "live" return value from a field or variable.
The appropriate documentation is here; in particular:
Return(field) doesn't work (it makes a copy of the field's current value when the action is defined)
Return(ByRef(field)) also doesn't work (it does exactly the same as above, contrary to what you might expect)
ReturnRef(field) doesn't compile (because the return type isn't a reference)
ReturnPointee(&field) does work (it returns the value as of the time the method is actually called)
Of course, you have to ensure that the pointee remains valid whenever the method is called, since it's now being used directly instead of making a copy.
I am coming from the C++ world and i want to do some simple stuff with Actionscript 3.0.
Have search around this site and google and haven't found a universally accepted way to do so. I will give you the C++ code of the analogous of what I am trying to do in Actionscript 3.0.
Pass by reference:
void somefunction (string &passvariable);
Create instance of, deep copy:
string something;
string somethingelse;
something = "randomtext";
somethingelse = something;
Pass by reference
Every object is passed by reference. As far as I know, there are no explicit & address of or * dereference operators. Actionscript is a higher level language than that.
Primitive types (and Strings are primitive - see link) are Immutable in Actionscript, so pass by value / pass by reference are effectively the same.
Deep Copy / Instance of
ObjectUtil.clone / ObjectUtil.copy will create sometimes-deep copies of Objects, if you're working in Flex. I usually don't rely on it for anything deep, however. In most cases you will want to create your own clone style method to create a deep copy.
A generic, flexible clone method can be found here
The rules for pass as reference are different for simple data types like string and number than they are for objects and complex data types.
If you are passing a string to a function, it creates a copy, leaving the original untouched.
So to pass by reference, try creating an object:
var str:Object = {string:"foo"};
passByref(str);
trace(str.string);
private function passByref(str:Object):void
{
str.string = str.string + "bar";
trace("inside", str);
}
As for deep object cloning, this works great:
package
{
import flash.utils.ByteArray;
public class DeepCopyUtil
{
public static function clone (source : Object) : *
{
var array : ByteArray = new ByteArray ();
array.writeObject (source);
array.position = 0;
return array.readObject ();
}
}
}
Credit where credit is due:
http://cookbooks.adobe.com/post_How_to_create_deep_copies_of_objects_and_arrays-19261.html
In Actionscript you have to define all things with function, var or const.
You should define the (return type) after the variable name, like var:String
Creating a function
function someFunction (var:String):void
{
}
Copy a string
var something:String;
var somethingElse:String;
something = "randomtext";
somethingelse = something;