Request: access with default value.

[smoofproof]

Hi everyone!

I would suggest to provide new member functions

    template <typename T>
    T operator ()(const typename object_t::key_type& key, const T &fallback) const
    {
        const auto it = find(key);
        if (it == end() || it.value().is_null())
        {
            return fallback;
        }
        else
        {
            return at(key);
        }
    }

    string_t operator ()(const typename object_t::key_type& key, const string_t &fallback) const 
    {
        return operator()<string_t>(key, fallback);
    }

    template <typename T>
    T operator ()(const typename object_t::key_type& key, const T &fallback)
    {
        const auto it = find(key);
        if (it == end() || it.value().is_null())
        {
            return (*this)[key] = fallback;
        }
        else
        {
            return (*this)[key];
        }
    }

    string_t operator ()(const typename object_t::key_type& key, const string_t &fallback)
    {
        return operator()<string_t>(key, fallback);
    }

I use those for convenient accesses to numbers, strings, vectors and maps in a json object with default values.

Further, i use

    reference operator()(const typename object_t::key_type& key)
    {
        return (*this)[key];
    }

    value_type operator()(const typename object_t::key_type& key) const
    {
        if (find(key) == end())
        {
            return value_type();
        }
        else
        {
            return (*this)[key];
        }
    }

for more consistent code look when using the functions above.

What do you think?

Greetings

[nlohmann]

This sounds related to the value function: https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a407e73a037e6e3067ef7aa2c25a79f39.html#a407e73a037e6e3067ef7aa2c25a79f39

[nlohmann]

@SmoofBullet Did you have the time to look at the value function?

[zumm]

@nlohmann method "value" helps to avoid outing of range only. If requested field exists, but has different type then this method throws exception. Such behavior is undesirable.

[nlohmann]

There has been quite a discussion about this, see #278.

[zumm]

So this functional will be implemented in release 3.0.0? Great (apropos when it happens?)!

[nlohmann]

#278 is planned for the 3.0.0. This release will most likely not be ready this year.

If you can live with the proposal in #278, I would like to close this ticket.

[zumm]

Yes, i can. :) But could starter of this ticket?

[nlohmann]

Oh, sorry. @SmoofBullet What do you think?

[smoofproof]

I think the solution will work for me, although im not sure whether the value function should be restricted to object types. If i provide a default value, i would not mind if the caller passed me the wrong type (something different than object).