Design Decisions

January 10, 2023 · View on GitHub

Require C++17
Initialiser Lists
Omitted Functions

This library is designed for correctness and simplicity, is based on C++ standard containers, and strives for speed through minimalism (rather than complicated optimisations).

Require C++17

For the first three years this library was compatible with C++11, however we changed the required standard version to C++17 before reaching version 1.0.0. There were two main reasons for making this change.

With C++11 the library had to include and maintain implementations of std::optional and std::string_view; the latter was not a full replacement since C++11 std::string does not know about string views.
Many places throughout the library that benefit from being able to use C++17 language features; for examples look at the flock of C++17-related commits made after the standards upgrade in October 2018.

Initialiser-Lists

The Value constructor that accepts an initialiser-list as argument will always (attempt to) create a Value that is an Object, i.e. it will never attempt to create a Value that is an Array, because it is not possible for the same function to accept initialiser-lists for both Arrays and Objects without introducing ambiguities:

Is { { "hallo", 1 }, { "world", 2 } } an Array with two Arrays as elements, or an Object with two members?
If foo has a default key in the traits, is { foo } an Array with one element, or an Object with one member?

Creating an Array from an initialiser-list is still possible with the static tao::json::value::array() function.

Omitted Functions

Class tao::json::value has neither a size() nor an empty() method due to the lack of unambiguous canonical semantics.

Should atomic JSON Values have size 0 or size 1, or should everything except for Null have size 1?
Should special values (like UNINITIALIZED) have size 0, or should they throw when checking the size?
Should strings use container semantics for size() and empty(), or should they behave like atomic Values?
Should a Value Pointer have size 1, or should it forward size() and empty() to the pointee Value?
Should an Opaque Pointer have size 1, or should it report the size of the JSON representation of the pointee?