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Can a core constant expression contain an ignored reinterpret_cast?


By : Robert Downey
Date : July 31 2020, 12:00 AM
Does that help A core constant expression cannot contain a reinterpret_cast even if its value is discarded (so MSVC and Clang are right to reject the code). See C++17 [expr.const]/2.15:
code :
enum {
    Value = 1 || reinterpret_cast<uintptr_t>(&x);  // OK
}


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What is a core constant expression in the C++11 Standard?


By : Programmer_N_Progres
Date : March 29 2020, 07:55 AM
Does that help N3690 does define the term "core constant expression in 5.19p2 [expr.const]:
code :
const double x = 2.;
constexpr double y = x;
constexpr double x = 2.;
constexpr double y = x;

`core constant expression` vs `constant expression`


By : Jaryl Chong
Date : March 29 2020, 07:55 AM
To fix the issue you can do The definition of a core constant expression depends on the concept of a constant expression as can be seen in bullet points (2.7.1) and (2.9.1) of N4140. , The definitions are mutually recursive, but not actually circular.

Why doesn't an if constexpr make this core constant expression error disappear?


By : unwabuisi
Date : March 29 2020, 07:55 AM
will be helpful for those in need The standard doesn't say much about the discarded statement of an if constexpr. There are essentially two statements in [stmt.if] about these:
In an enclosing template discarded statements are not instantiated. Names referenced from a discarded statement are not required ODR to be defined.
code :
template <typename T>
void f() {
    constexpr int x = -1;
    if constexpr (x >= 0){
        constexpr int y = 1<<x;
    }
}
template <typename T>
void f() {
    constexpr T x = -1;
    if constexpr (x >= 0){
        constexpr int y = 1<<x;
    }
}
int main() {
    f<int>();
}

Core constant expression and array indexing


By : Jawwad
Date : March 29 2020, 07:55 AM
may help you . Supporting variable-length arrays is a compiler extension, which the standard generally permits as long as it doesn't make conformant code behave differently, and as long as they say that it's an extension (which GCC does with that warning):

Is there a constant expression that is not a core constant expression?


By : Phillip Archer
Date : March 29 2020, 07:55 AM
should help you out [expr.const]/5 defines "constant expression" as:
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