CODEWITHSUNDEEP
c++boost-variantboost-any
paperjam
paperjam

Reputation: 8528

C++ container of any/variant each element having unchanging type

I am using std::map<const char*, boost::any> to store my library's settings. Each setting only uses a single underlying value type and I want to enforce this during configuration calls to set() or similar. Settings are initialized with default values of the correct type.

Here is some pseudo code that hopefully shows what I'm trying to achieve:

using namespace std;
using namespace boost;

void set(map<const char *, any> &settings, const char *key, any &value)
{
    if (type_of(value) != type_of(settings[key]) throw wrong_type_exception();
    settings[key] = value;
}

Is it possible to trap type errors like this at runtime? I'd prefer not to have template functions in my API if possible.

I've used boost::any but might consider boost::variant's which() if that's the only viable solution.

Upvotes: 1

Views: 263

Answers (1)

Steve Jessop
Steve Jessop

Reputation: 279335

value.type() != settings[key].type()

If settings[key] doesn't previously exist, then settings[key].type() is typeid(void), which compares equal to value.type() if and only if value is empty. So you won't be able to add new setting/value pairs via this function, but based on the pseudo-code that seems to be intended.

Upvotes: 2

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