CODEWITHSUNDEEP
c++
user2738709
user2738709

Reputation: 3

Map string to different classes based on that input string

I am trying to create a C++ map with following template

map<string,class> mapper;

where mapper will contain following data

mapper['a'] = Class A or object of Class A
mapper['b'] = Class B or object of Class B
mapper['c'] = Class C or object of Class C

What should be the template of the mapper for this kind of map where Class is selected based on the input string?

Upvotes: 0

Views: 398

Answers (1)

Vittorio Romeo
Vittorio Romeo

Reputation: 93264

Assuming that the strings are only known at run-time and that you can build an hierarchy of classes, the easiest option is using polymorphism and std::function in order to build a map of factory functions:

Given...

struct Base
{
    virtual ~Base() { }
};

struct Derived0 : Base { };
struct Derived1 : Base { };
// ...

...you can have...

std::map<std::string, std::function<std::unique_ptr<Base>>> map;

map["derived0"] = []{ return std::make_unique<Derived0>(); };
map["derived1"] = []{ return std::make_unique<Derived1>(); };
// ...

...which can be used as follows:

std::string desiredType;
std::cin >> desiredType;

auto result = map[desiredType]();

Note that this kind of design usually is a code smell. Think carefully about what you want to achieve - there probably is a cleaner/more elegant way of doing it.

Also, using std::unique_ptr and std::function may introduce noticeable overhead in your application.

Upvotes: 1

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