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Showing content from https://en.cppreference.com/w/cpp/language/../error/../language/../types/type_info/hash_code.html below:

std::type_info::hash_code - cppreference.com

Returns an unspecified value (here denoted by hash code) such that for all std::type_info objects referring to the same type, their hash code is the same.

No other guarantees are given: std::type_info objects referring to different types may have the same hash code (although the standard recommends that implementations avoid this as much as possible), and hash code for the same type can change between invocations of the same program.

(none)

A value that is identical for all std::type_info objects referring to the same type.

The following program is an example of an efficient type-value mapping without using std::type_index.

#include <functional>
#include <iostream>
#include <memory>
#include <string>
#include <typeinfo>
#include <unordered_map>
 
struct A
{
    virtual ~A() {}
};
 
struct B : A {};
struct C : A {};
 
using TypeInfoRef = std::reference_wrapper<const std::type_info>;
 
struct Hasher
{
    std::size_t operator()(TypeInfoRef code) const
    {
        return code.get().hash_code();
    }
};
 
struct EqualTo
{
    bool operator()(TypeInfoRef lhs, TypeInfoRef rhs) const
    {
        return lhs.get() == rhs.get();
    }
};
 
int main()
{
    std::unordered_map<TypeInfoRef, std::string, Hasher, EqualTo> type_names;
 
    type_names[typeid(int)] = "int";
    type_names[typeid(double)] = "double";
    type_names[typeid(A)] = "A";
    type_names[typeid(B)] = "B";
    type_names[typeid(C)] = "C";
 
    int i;
    double d;
    A a;
 
    // note that we're storing pointer to type A
    std::unique_ptr<A> b(new B);
    std::unique_ptr<A> c(new C);
 
    std::cout << "i is " << type_names[typeid(i)] << '\n';
    std::cout << "d is " << type_names[typeid(d)] << '\n';
    std::cout << "a is " << type_names[typeid(a)] << '\n';
    std::cout << "*b is " << type_names[typeid(*b)] << '\n';
    std::cout << "*c is " << type_names[typeid(*c)] << '\n';
}

Output:

i is int
d is double
a is A
*b is B
*c is C

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