Would be good to get some words about performance. Looking at the code there are a lot of granular memory allocations, which IME with other JSON libraries which work like this is the number one performance killer and can add up to seconds when parsing JSON files with hundreds of thousands of nodes.

Always going through a 'virtual method table' also can't be great for performance (not so much because of the indirection, but because it acts as an optimization barrier for the compiler).

Peformance doesn't matter much of course when the code is ever only used to load tiny JSON files.