variant

The pattern that a lot of people use with C++17 / boost variants looks very similar to switch statements. For example: ( snippet from cppreference.com ) std::variant<int, long, double, std::string> v = ...; std::visit(overloaded { [](auto arg) { std::cout << arg << ' '; }, [](double arg) { std::cout << std::fixed << arg << ' '; }, [](const std::string& arg) { std::cout << std::quoted(arg) << ' '; }, }, v); The problem is when you put the wrong type in the visitor or change the variant signature, but forget to change the visitor. Instead of getting a compile error, you will have the wrong

I keep seeing the phrase "duck typing" bandied about, and even ran across a code example or two. I am way too lazy busy to do my own research, can someone tell me, briefly: the difference between a 'duck type' and an old-skool 'variant type', and provide an example of where I might prefer duck typing over variant typing, and provide an example of something that i would have to use duck typing to accomplish? I don't mean to seem fowl by doubting the power of this 'new' construct, and I'm not ducking the issue by refusing to do the research, but I am quacking up at all the flocking hype i've

when I'm looking at the "Variant Data Type" documantation, it says that variant with subtype of double can support a positive value of maximum "1.79769313486232E308" (15 digits) and that "An error occurs when Variant variables containing Currency, Decimal, and Double values exceed their respective ranges." However, when I'm running the following code: y = 999999999999999999999999999 y = CStr(CDBL(y)) MsgBox y I do not recive an error, instead I am getting a msgbox with the following output: "1e+27" (27 is the number of digits in y). What is the explantion to this? how is "y" stored in the

I am trying to experiment with std::variant. I am storing an std::variant as a member of a class. In the below code, things work fine if the variant is stored by value, but does not work (for the vector case, and for custom objects too) if the variant is stored by reference. Why is that? #include <variant> #include <vector> #include <iostream> template<typename T> using VectorOrSimple = std::variant<T, std::vector<T>>; struct Print { void operator()(int v) { std::cout << "type = int, value = " << v << "\n"; } void operator()(std::vector<int> v) const { std::cout << "type = vector<int>, size =

I'm using a function in vbscript which returns a variant array of strings. JobIDs = objDoc.ConnectedSubmit(objServer) The problem is I can't get the Job ID values from that array, as vbscript doesn't handle typed variables. It just gives a type mismatch when I attempt to do ANYTHING with the JobIDs array. I found some promising information here , but when I used the conversion function: Set objConverter = CreateObject("ADS.ArrayConvert") ConvertedJobIDs = objConverter.CStrArray(JobIDs()) It is giving me the same type mismatch error. Am I missing something obvious here? This is, apparently, an

How to convert a byte array to Variant? I have a WebService that should receive an array of byte, but it only accepts variable of type VARIANT, I wonder how to convert in order to pass it as parameter for Web Services. thank you According to the comment trail, you need to create a SAFEARRAY of bytes. Which is done like this in Delphi: V := VarArrayCreate([0, N-1], varByte); Or, if the SAFEARRAY needs 1-based indexing: V := VarArrayCreate([1, N], varByte); You can then populate the array in a loop using V[i] := ... . If you have a Delphi dynamic array of Byte , and the expected SAFEARRAY uses 0

Is it permitable to design std::optional (currently std::experimental::optional ) in such a way, that for trivially default constructible type T corresponding std::optional< T > is also trivially default constructible? The same question regading std::variant and its integral discriminator. My own answer is: "No, it cannot be designed in this way, because value of its integral discriminator obtained during default initialization will be indeterminate if the object has automatic storage duration or if it is reinterpret_cast -ed from non-zero-initialized storage." Requirement to the user to do

I'm working with a COM object that returns a multidimensional VARIANT array (vt_array), and I'm trying to read values from the array. When I use print_r($mdArray) it displays variant Object . ( variant_get_type($mdArray) returns 8204 .) I tried using foreach ($mdArray as $oneArray) but I get the message: Warning: Loader::getfields() [loader.getfields]: Can only handle single dimension variant arrays (this array has 2) in C:\Inetpub\wwwroot\root\script\fileloader.php on line 135 Fatal error: Uncaught exception 'Exception' with message 'Object of type variant did not create an Iterator' in C: