How to create a container of functions?

[JUAN DENT]

Hi,

I need a container of functions (like a vector for example). But each function may be different than the others although they all return the string type. They differ in the parameter type, like so:

std::string to_string(int value)
std::string to_string(double value)
// etc... 

These functions are meant to format the value into a table cell as text. It might be necessary to specify formatting flags as well.

Any ideas?

Regards,
Juan Dent

[jlb]

Normally an array of functions require the same type and number of parameters.

Why can't you just use "normal" C++ overload mechanisms? For example your above snippet should just used as normal overloads.

But be careful there is already a standard function called to_string(), and using the prefix "to_" should be avoided when possible as there are quite a few standard functions that start with this prefix.

[TheIdeasMan]

Hi,

Not sure if this will work for you:

https://stackoverflow.com/questions/37904897/a-container-of-stdfunction-with-polymorphic-types-as-function-arguments

Basically it's a std::unordered_map of std::unique_ptr to std::function

IIRC std::function can be any callable target

Good Luck !! :+)

[mbozzi]

One can work with entire overload sets by having a function object with an overloaded operator()():
For example:

constexpr struct my_to_string_t 
{
  std::string operator()(int x) const { return std::to_string(x); } ;
  std::string operator()(double x) const { return std::to_string(x); };
  // ...
} my_to_string;

// ...
my_to_string(2.0);
my_to_string(42);

If the collection really needs to be modifiable at run-time, then I think you have to use some trickery like @TheIdeasMan suggests.

[JUAN DENT]

Thanks for the ideas!!