Inconsistency between operator[] and push_back

[nlohmann]

Situation

When operator[] is called on a null value with a string_t argument, the value is silently converted to an object. When operator[] is called on a null value with an integer argument, an exception is thrown.

This feels inconsistent compared to push_back: When push_back is called on a null value, the value is silently converted to an object (if the argument was a string_t/json-pair) or an array (if the argument was a json value).

Proposal

I would propose changing operator[] to always convert a null value to an array. Thereby, the following code would be possible:

json j;
j[2] = 17;
std::cout << j << '\n';

And the output would be [null,null,17].

Rationale

This would then behave exactly like the following code:

json j = json::array();
j[2] = 17;
std::cout << j << '\n';

This code already works as described: Calling operator[] on an array, but with an integer argument out of bounds extends the array accordingly with null values.

What do you think?

[gregmarr]

To be clear, do you mean changing this only for integer arguments?

[nlohmann]

I was wrong: the non-const versions of operator[] both convert null values to array/object, whereas the const versions throw when applied to a null value. That is, the behavior is OK, and apart from some copy/paste errors in the documentation, everything is fine.

When I opened this issue, I was entirely working with the documentation, got confused, but did not check the source code (which I should have done in the first place...).

Nothing to see here, carry on :-)