Compile-Time

Tag Dispatch or if constexpr

Difficulty

Asked at Flow Traders, Maven Securities

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xxxxxxx xxxx xxxxxxxxxx xxxxx xx xx xxxxxxxxx xxxxxx xxx xxxxxxxxx xxxxx, xxx x xxxxx xx xxxxxx xxxxxxx xx: xxxx xxxxxxxx xx xx xx xxxx xx xxxxxxx xxx xxxxx x xxxx xxxxxxx xxxx, xxx xxxxx.xxxx_xxxx() xxxx xxx xxxxxxx xxx xx xxx. xxxxxxxxx xxx xx xxxx xxx xxxxxx xxxxxx xxxxxxxxxxxxx. x++ xxx xxxxx xxxxxxxxxx xxx xxxx, xxxx xxxxx xxxxxxxxx xxxx, xxx xxx xxxxxxxx xx xxx xxxxx xxx xx xxxx. xx xx xxxx xxxx xxx xxxxx xxx xxxx xx xx xxx xxxxx xxxx. xxxxxxxxx xxxx_xx xxxxx xxxxx, xx xxxxx xxxxxxxxxx. xxx xxxxx xxxx xxxxxx: xxxxxxxxxxxx xxxx xxxx xxxx_xxxx()xxxxx.xxxx_xxxx()xx xxxxxxxxxx xxxxxxxxxx(x)xxxxxxxx xxxxx x. xxxx::xxxx_xx: xxx xxxxxxxx. x xxxxx xxxx x xx xxx xx xxxxx xxxxx xxx xxxxx, xxx xxxxxxxx xxxxxxxxxx xxxxx xxx xxxxxxxx. xxx xxxx xxx xxxx xxxxxx x++xx. x. xxxxxx::xxxx_xx: xxx xxxxxxxx, xx xxxxxxxxx. x. xxxxxxxxxxx::xxxx_xx: xxxxxxxxxxx xxxxxxxxx, xxxx xxx xxxxxxxxxx xx xxx xxxxxxxxxxxx. x xxxxxxxxxxx xxxxxxx xx xxxxxxxx xx xxx xxxxx xxx xxx xxxx xxxxxxxx xxx xxxxxx xxxx xx xxx xxxx xxxxxx xx. xxxxxxxx xxxx::xxxx_xx(xxxxx{}); // xx xxxxxx::xxxx_xx(x.x); // x xxxxxxxxxxx::xxxx_xx(xxxxxx{}); // x xxx xxxxx xxxxxx xxxx xxx xxxxx xxxxx xx xxxxx xxxxx, xxxxxxxxx xxxxx xxxx xx xxxxxxx xx xxx. xxxxxxxxxxx xxxxx xxxxxxx xxxx xxxxxxx xxx xxxxx xxxx, xxxxxxxxx xxx::xxxxxx xxx xxxxxx, xxxxx xxxxx xxxx xx xxx xxxxxxxxxx. xxx xxx xxxxx xxxx xx xxxxx. x xxx xxxxxx xx xxxxx x xxxxxxx-xxxx xxxxxx xxxx xx xxxxxxxx xxx; xx xxxxx xxxxxxx xxx xxxxx xxxxxxx xx xxx xxxx. xxx xxxxxxxxxxx xxxxxxxxx xxxx xx xx xxxxxxxx xxxxxxxxx. xxx xxxxxxxxx xxxxx xxxxxxxxxxx xxxxxxx xxxxxxx xxx xxxxx xxx xxxxxxxxx xxx x xxxx xxxxxxxxxx xxxx, xxx xxx xxxxxxxx xxxx xxx xx xxxxxxx xxxxxxxxxx xxx. xxxxxxx xxxx xxx x xxx-xxxx xxxxxx. xxx xxxxx xxxxxxx xx xxxxxxx xxxx xxx xxxx xxx xxxxx xxxx xxxx.

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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