What is the typical usage of boost any library?

Question

What are the advantages of using boost.any library ? Could you please give me some real life examples ? Why the same functionality couldn\'t be achieved by having some gener

Answer 1

We use boost.any as the carrier type for a type-safe tagged variadic container. Here's what that means:

We have a "raft" object, which travels through a set of filters. When a filter wants to add data to the raft, it can do something like this:

raft.addTaggedData<ETag1>(3.0);
raft.addTaggedData<ETag2>("a string")`;
std::string str = raft.getTaggedData<ETag2>();
int a = raft.getTaggedData<ETag1>(); // <-- Compile error

Where ETag1 and ETag2 are members of an enum, and we use a traits template to map tags to types.

The raft class is using a list of pair<ETagType, boost::any> as a backing store. Boost.any saved us the pain of managing raw buffers for various types.

Answer 2

Why the same functionality couldn't be achieved by having some generic type in the root of object's hierarchy and creating containers with that base type ?

That calls an object hierarchy -- a construct you are injecting in artificially in to the design for solving a peripheral problem. Further, such a construct is easy to get wrong and a wrong implementation can wreak havoc. Boost.Any is a community reviewed safe, well-tested alternative.

Could you please give me some real life examples ?

TinyJSON uses boost.Any.

What are the advantages of using boost.any library ?

I refer the introductory documentation.

Answer 3

boost::any will happily store ints and floats, types that clearly have no base classes. A real-life example where you can use it is a virtual machine for a high-level interpreted language. Your "function" objects will need an array of arguments. This can easily be implemented with a std::list<boost::any> behind the scenes.

Answer 4

I consider that Boost.Variant should always be preferred as it's non-intrusive and still calls for very structured programming.

But i guess the main idea behind boost.any is to provide the equivalent of java and c# object types. It's a way of saying "yes we can" ! :-)

Answer 5

We've used it in a property map, (std::map<std::string, boost::any>), to store a lot of things dynamically in a simple, flat dataspace.

Mostly we either stored smart-ptr-to-scriptable-objects or strings, but some entries where other types (floats, vec3f, matrices, and other non-standard objects).

It works pretty well for adding more dynamic capabilities to c++, or wherever you want some type-erasure to just add any type of data to an object.