For the optional mapping example a `void age(IDL::optional<float>&&)` is lacking, like described for some types in chapter 6.14

For the example code, for the setter, the std::optional should be passed as const&, see https://stackoverflow.com/questions/69277649/does-passing-an-stdoptionalt-by-reference-actually-save-copying

Within the text of chapter 6.31/6.32 (IDL4) all C++/IDL should use a different font to make it clear it is code, just as in the other chapters.

For anyone using the class mapping of a structure the spec should also provide a class mapping for a bitset, that way they have a consistent API. Also why is a inherited bitset not mapped to C++ inheritance, by removing the inheritance the inheritance relation can't be used in C++ also

The spec defines the type trait bit_bound as `std::integral_constant<uint32_t, b>`, but as bit_bound is maximal of 64, this could be `std::integral_constant<uint8_t, b>`

The bitmask mapping is very basic, it doesn't give any type safety or more modern API. The spec should be improved, the <X>Bits type should be removed, only one type should be used. Also when there are multiple bitmasks with the same bitfield name they could result in a name clash. Maybe map to a enum class and add the operators ~,|,^,& for the enum class as inline operations to modify the enum class as a bitmask. At that moment the Bit type can be removed.

When time permits I will make a proof of concept for TAOX11

The spec should mention how the IDL4-mentioned annotations impact the mapping, I think the spec should list at least @value, @default_literal, @default, @range @min @max @bit_bound @external

See IDL4 to CPP and the IDL4 spec itself

Instead of `VariableExt(const Variable&, bool);` it should be `VariableExt(Variable, bool);` so that in the implementation we can use std::move, this is as all complex types are passed into the constructor of a struct

The bit_bound annotation can be applied to the enum, so the bit_bound and underlying_type traits should also be added to the enum

The section says:

"For all primitive types, enums, and
reference types, an in argument A of type P, that argument is passed as P. For all other types, an in argument A of type P is
passed as const P&. For an inout and out argument it is passed as P&. If we return a type of P, it is returned as P."

This is the only use of "primitive types" in the spec. "Basic Data Types" should be preferred. Would suggest:

"For all Basic Data Types [link/ref to 6.6 Mapping for Basic Data Types], enums [link/ref to 6.9 Mapping for Enums], and
reference types [link/ref to 6.7.1 Reference Types], an in argument A of type P, that argument is passed as P. For all other types, an in argument A of type P is
passed as const P&. For an inout and out argument it is passed as P&. If we return a type of P, it is returned as P."

This chapter says:

The Fixed(std::string&) constructor converts a string representation of a fixed-point literal, with an optional leading sign (+ or -) and an optional trailing ‘d’ or ‘D’, into a real fixed-point value.

But there is no constructor that accepts a non-const std::string&, the text should say

The Fixed(const std::string&) constructor converts a string representation of a
fixed-point literal, with an optional leading sign (+ or -) and an optional trailing ‘d’ or ‘D’, into a real fixed-point value.

Double "to to" in the first sentence:

IDL bitset types are mapped to to C++ structs that meet the C++11 requirements for aggregate initialization.

Should be

IDL bitset types are mapped to C++ structs that meet the C++11 requirements for aggregate initialization.

In the specification an addition was made about the default argument when the union member has multiple legal discriminator values:

Union members associated with the "default" label and those associated with multiple labels may have multiple legal discriminator values. For these members, the modifiers (those that return void) have a second parameter which has the discriminator's type. This parameter has a default argument. For members associated with multiple labels, the value of the default argument is the value of the case label that appears first in IDL. For members associated with the default label, the value of the default argument is an implementation-defined value that selects the member.

There is nothing in the text that describes what happens when a discriminator value is passed which doesn't belong to the member, this is implicitly in the example code further down "u.obj(a, 2)", but this should be explicit in the text also, passing a not allowed discriminator should result in a BAD_PARAM exception

For some use cases it would be more efficient to map a IDL map to a std::unordered_map (see https://en.cppreference.com/w/cpp/container/unordered_map), maybe standardize an annotation which can be used to override the mapping to std::map to the type as specified by the annotation?

using M2 = IDL::bounded_map<std::string, T, 20;

should be

using M2 = IDL::bounded_map<std::string, T, 20>;

The spec has the following sentence:

The _d discriminator modifier can only be used to set the discriminant to a value within the same union member.

This is not really clear and should be improved, maybe

The _d discriminator modifier can only be used to set the discriminant to a value that has the same union member as currently selected.