std::multimap¶

Ruby does not natively provide MultiMaps. Thus Rice wraps std::multimap.

Rice will automatically define Ruby classes for each instantiation of std::multimap it finds. You may also manually define Ruby classes via the use of the define_multimap method. Multimap classes are added to the Std module.

Usage¶

For C++ methods that take multimap arguments, you can instantiate a new multimap from Ruby (see Automatically Generated Ruby Classes).

For example, assume this C++ code:

void passMultiMap(std::multimap<std::string, int> stringMultimap)
{
}

define_global_function("pass_multimap", &passMultiMap);

One way to call it from Ruby is like this:

multimap = Std::Map≺string‚ int≻.new
multimap["thrity seven"] = "thirty seven"
pass_multimap(multimap)

In this case, Ruby is wrapping a C++ multimap. Therefore any changes made to the multimap in C++ will be visible to Ruby.

A second alternative is to pass it a Ruby hash instead:

hash = {"three" => 3, "five" => 5, "nine" => 9}
pass_multimap(hash)

In this case, Rice will copy the Ruby hash instead of wrapping it. Thus any modifications made in C++ will not be visible to Ruby.

Ruby API¶

Rice tries to make std::multimap look like a Ruby Hash by giving it an API that is a subset of Hash. However, there are differences you need to keep in mind.

First, the following methods only work if the multimap type is copyable (copying is done in C++):

multimap#copy(other)

Second, the following methods only work if the multimap type implements C++’s equal operator, operator==:

multimap#value?

Third, if the multimap type supports C++ streams, then the following method will work, otherwise it will return “Not Printable”

multimap#to_s