CODEWITHSUNDEEP
c++c++14dryvariadic
Charles
Charles

Reputation: 11499

Calling a function with a vector of arguments

I have a std::vector of arguments and I would like to call a function with them. Is there any way to do this?

In particular the function is the mysqlx select function and the arguments are the columns I'm trying to query; they will all be of type std::string. The purpose of the function is to reduce duplication in the codebase.

(This seems like a generally useful topic, but I could not find an answer through search. If I missed it and this has already been answered, please point me to the question and close this as a duplicate, thanks.)

Upvotes: 2

Views: 1117

Answers (1)

Caleth
Caleth

Reputation: 63392

You can do it, up to a compile time maximum number of arguments. It isn't pretty.

using result_type = // whatever
using arg_type = // whatever
using args_type = const std::vector<arg_type> &;
using function_type = std::function<result_type(args_type)>;

template <size_t... Is>
result_type apply_vector_static(args_type args, std::index_sequence<Is...>)
{
    return select(args[Is]...);
}

template<size_t N>
result_type call_apply_vector(args_type args)
{ 
    return apply_vector_static(args, std::make_index_sequence<N>()); 
}

template <size_t... Is>
std::map<size_t, function_type> make_funcs(std::index_sequence<Is...>)
{
    return { { Is, call_apply_vector<Is> }... };
}

result_type apply_vector(args_type args)
{
    // Some maximum limit
    static const auto limit = std::make_index_sequence<50>();
    static const auto funcs = make_funcs(limit);
    return funcs.at(args.size())(args);
}

See it live

Upvotes: 4

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