CODEWITHSUNDEEP
c++c++11boostvectorstl
Manea Flavian Costin
Manea Flavian Costin

Reputation: 49

How to iterate over boost::variant<std::vector<int>, std::vector<String>>?

as the title is pretty explanatory, how is the best way to iterate over a boost::variant<std::vector<int>, std::vector<string>> variable?

Say that I have a structure:

struct foobar{
    enum typeOfVariant {intVariant, StringVariant}
    boost::variant<std::vector<int>, std::vector<String>> variable;
    }

That i receive at a certain point with the guarantee that the enum is corelated with the type from the variant.

To achieve maybe something like:

boost::variant<std::vector<int>, std::vector<string>> var;

for (auto t in var)
{
//do something
}

^this might be the ideal way.

Or to force conversion to a std::vector<int> or std::vector<string>, based on the enum type?

Upvotes: 1

Views: 1044

Answers (1)

Yakk - Adam Nevraumont
Yakk - Adam Nevraumont

Reputation: 275260

In C++14:

apply_visitor( var, [&](auto&& var){
  for( auto&& t : var ) {
    // code goes here
  }
});

There is no need for the enum. Variants know what type they have within themselves.

A variant is a union and an index into the correct type in the union. that index is basically your enum.

We can do it externally with an if block and two versions each of which assumes the content is one type or another, or similar, but that adds bulk, and rarely adds value.

Most nominally C++11 compilers can handle the above. Without it you have to either write a function object class manually that replicates it, or you could use the "conditional cast"s and write the loop twice, one for each type.

What can I say, C++14 solved problems.

Upvotes: 1

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