What does [] operator means for map

Question

Hi

As we all know that subscript operator [] helps to identify the element into sequential container...

However , we can use this [] for map insert functionality as below:

mymap[key] = value;

I am trying to find out how we can implement the same functionality in custom user defined map..

Any hint would be useful... I tried to use operator [] and can also get "key" from function argument but how to take "value" into function?

Current source code is as below :
https://code.sololearn.com/cJWK6P984Ab5/?ref=app

Feel free to provide any improvement on the source code.. one known point is yet open that everything is public in data due to struct and later on will strict it with access specifier..

Answer 1

1.using type aliases
First add these 2 typedefs to struct node
typedef U value_type;
typedef value_type& reference;

The [] will then be

typename node<T,U>::reference
operator[](const T& key)
{
//return value if key is found
//else add the key and default
//value to the map

auto res=(this->search(key));
if(res) return res->value;
else return
(this->insert(key,U{}))->value;
}

2.using trailing return type syntax
auto
operator[](const T& key)
->decltype(node{key,declval<U>()}.value)&
{
//return value if key is found
//else add the key and default
//value to the map

auto res=(this->search(key));
if(res) return res->value;
else return
(this->insert(key,U{}))->value;
}

Answer 2

Thanks Anthony Maina