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Mar 10, 2024
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Update metafunctions.md #1015

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16 changes: 14 additions & 2 deletions docs/cpp2/metafunctions.md
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Expand Up @@ -28,7 +28,7 @@ point2d: @value type = {

## <a id="generating-source"></a>Generating source code at compile time

A metafunction applied to a definition using `@` gets to participate in interpreting the meaning of the definition by inspecting and manipulating the definition's parse tree. For example
A metafunction applied to a definition using `@` gets to participate in interpreting the meaning of the definition by inspecting and manipulating the definition's parse tree. For example:

``` cpp title="shape.cpp2: Using @interface @print" hl_lines="1"
shape: @interface @print type = {
Expand Down Expand Up @@ -128,6 +128,17 @@ A `basic_value` type is a regular type: [`copyable`](#copyable), default constru

A `value` (or `weakly_ordered_value` or `partially_ordered_value`) is a `basic_value` that is also [`ordered`](#ordered) (or `weakly_ordered` or `partially_ordered`, respectively).

```mermaid
graph TD;
value---->basic_value;
weakly_ordered_value---->basic_value;
partially_ordered_value---->basic_value;
basic_value-->copyable;
value-->ordered;
partially_ordered_value-->partially_ordered;
weakly_ordered_value-->weakly_ordered;
```

These metafunctions will emit a compile-time error if:

- any function is protected or virtual
Expand All @@ -142,6 +153,7 @@ These metafunctions will emit a compile-time error if:
>
> — P0707R4, section 3


#### `struct`

A `struct` is a type with only public bases, objects, and functions, with no virtual functions, and with no user-defined constructors (i.e., no invariants) or assignment or destructors.
Expand Down Expand Up @@ -187,7 +199,7 @@ Cpp2 has no `interface` feature hardwired into the language, as C# and Java do.

- the type has a copy or move function (the diagnostic message will suggest a virtual `clone` function instead)

- any function has body
- any function has a body

- any function is nonpublic

Expand Down