template-instantiation | Template Instantiation is a new web platform feature | Web Services library
kandi X-RAY | template-instantiation Summary
kandi X-RAY | template-instantiation Summary
Template Instantiation is a new web platform feature with ongoing, developing proposals coming out of a few corners of the ecosystem.
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QUESTION
I have many functions q1, q2, q3, etc., each with a different return type (int, int64_t, std::string, etc.).
I also have a print_result function that prints out their results (and the time they take to run, but trimmed here for simplicity):
ANSWER
Answered 2020-Jul-10 at 10:19I've got a different proposal:
- Use an std::array instead of switch (or std::map if the switch cases are non-continuous, std::array has O(1) access time, std::map O(log(n)) and switch O(n).
- Use std::function and std::bind to bind your functions you want to call to a functor object
- use the index into the array to call the function
- Use placeholders if you need to pass additional data
QUESTION
I have several views in my app, that are almost the same, so I decided to create a CBaseView class and to not copy the code. So I have something like this:
...ANSWER
Answered 2020-May-19 at 07:21I don't know MFC, but the problem is quite clear: The macros do not accept template instantiations. This is understandable, because macros are expanded first and once you instantiate the template, you wont have CBaseView but something like CBaseView, ie concrete types for the parameter.
DECLARE_DYNCREATE is to enable creation of instances on the fly at runtime, while templates only exist at compiletime, so at some point you'll need to decide what instantiations of the template you want to use at runtime. You could keep the implementation in the template, but for the types used with the framework you use:
QUESTION
template< typename _Type >
struct TypeChecker {};
template< typename _Type >
bool f0( _Type obj )
{
return TypeChecker< _Type >::value;
}
struct S {};
void f1()
{
f0( S{} );
}
template<>
struct TypeChecker< S > : std::true_type {};
ANSWER
Answered 2020-Mar-08 at 15:17Your program is ill-formed, no diagnostic required, because the explicit specialization is not defined before the (first) place where it is (or would be) implicitly instantiated. The point of instantiation business is something of a red herring: that governs name lookup, not validity (except that it’s also ill-formed NDR to have the results of that lookup depend on which of multiple points of instantiation is chosen).
QUESTION
I am learning forcing template instantiantion.
It works, but I am still curious :-
ANSWER
Answered 2019-Sep-16 at 07:25Why the line #2# is enough to force instantiation?
To supply the second argument, the compiler has to bind a reference. Meaning it ODR-uses the static variable, so the variable has to exist and have a unique identity. Ergo, its definition is instantiated.
When you use plain int, the second parameter can only accept integer constant expressions. A non-const static is not usable in a constant expression.
Why do I need
int&as another template parameter to make it compilable?
You need to declare the type of the reference for the second parameter to have a type the compiler can check against. Well, prior to C++17 you needed to anyway. Nowadays we can use a placeholder type instead.
QUESTION
TL,DR: How can I force clang to export the symbols of implicitly instantiated functions even when -O3 is active?
Let's take the following code:
...ANSWER
Answered 2018-Sep-07 at 19:43Add attribute used, like this:
QUESTION
While trying to replicate the behavior in this question in Visual Studio 2017 I found that instead of linking &FuncTemplate to the exact same address the function template<> FuncTemplate() {} gets copied into dllA and dllB so that the corresponding test program always returns not equal.
The solution was setup fresh with 3 Win32Projects, one as ConsoleApplication, the others as DLL. To link the DLLs I added them as reference to the console project (linking manually didn't work either). The only change in code I made was adding the __declspec(dllexport) to a() and b().
Is this behavior standard conforment? It seems like the ODR should be used here to collapse the copies of the function. Is there a way to get the same behavior seen in the other question?
Template.h
...ANSWER
Answered 2017-May-08 at 21:18C++ compilation is generally split into two parts, the compiler itself and the linker. It is the job of the linker to find and consolidate all the compilations of an identical function into a single unit and throw away the duplicates. At the end of a linking step, every function should either be part of the linker output or flagged as needing to be resolved at execution time from another DLL. Each DLL will contain a copy of the function if it is being used within that DLL or exported from it.
The process of resolving dynamic links at execution time is outside of the C++ tool chain, it happens at the level of the OS. It doesn't have the ability to consolidate duplicates like the linker does.
I think as far as ODR is concerned, each DLL is considered a separate executable.
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