Tag Dispatch or if constexpr

Difficulty

Asked at Flow Traders, Maven Securities

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xxxxx	xxxxxx
x xxxx xxxx `xxxx_xxxx()`	`xxxxx.xxxx_xxxx()`
xx xxxxxxxxxx xxxx	`xxxxxx(x)`
xxxxxxxx xxxx	x

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Language: C++23size_of

#include <concepts>
#include <cstddef>
#include <string>
#include <type_traits>
#include <vector>

// ...
// ...
// ...

// ...
struct Quote {
    long long wire_size() const { return 24; }
};

struct Trade {
    long long wire_size() const { return 40; }
};

// ...
// ...

// ...
struct Opaque {
    int junk = 0;
};

// ...
// ...
template <typename T>
concept HasWireSize = requires(const T& value) {
    { value.wire_size() } -> std::convertible_to<long long>;
};

// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...

// ...
// ...
namespace tags {

struct has_member {};
struct is_number {};
struct neither {};

template <typename T>
using category_of = neither;  // ...

template <typename T>
long long size_of(const T& value) {
    // ...
    (void)value;
    return 0;
}

}  // ...

// ...
namespace branch {

template <typename T>
long long size_of(const T& value) {
    // ...
    (void)value;
    return 0;
}

}  // ...

// ...
// ...
namespace constrained {

template <typename T>
long long size_of(const T& value) {
    // ...
    (void)value;
    return 0;
}

}  // ...

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