When should I use std::any

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Since C++17 std::any is introduced. One can now write code like this

#include <iostream> #include <any> #include <string>  int main () {     const double d = 1.2;     std::any var = d;     const std::string str = "Hello World";     var = str; } 

A double is assigned to the variable var and than a std::string was assigned to it.

Why has std::any been introduced?

I think this is violating the least astonishment rule, because I find it hard to think of a situation, where this can be used to express more clearly, what I like to express.

Can somebody give me a good example, when std::any is beneficial.



When to Use
void* as an extremely unsafe pattern with some limited use cases, std::any adds type-safety, and that’s why it has some real use cases.

Some possibilities:

  • In Libraries - when a library type has to hold or pass anything without knowing the set of available types.
  • Parsing files - if you really cannot specify what are the supported types.
  • Message passing.
  • Bindings with a scripting language.
  • Implementing an interpreter for a scripting language
  • User Interface - controls might hold anything
  • Entities in an editor


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