Move field documentation to new file

Author: nickpdemarco

book/src/SUMMARY.md

@@ -7,6 +7,7 @@
   - [Name mapping](./call_rust_from_cpp/name_mapping.md)
   - [Wellknown traits](./call_rust_from_cpp/wellknown_traits.md)
   - [Layout policy](./call_rust_from_cpp/layout_policy.md)
+  - [Fields](./call_rust_from_cpp/fields.md)
   - [Types with special support](./call_rust_from_cpp/special_types.md)
   - [Panic and exceptions](./call_rust_from_cpp/panic_and_exceptions.md)
 - [Calling C++ from Rust](./call_cpp_from_rust/index.md)

book/src/call_rust_from_cpp/fields.md

@@ -0,0 +1,38 @@
+# Fields as underlying types
+
+When you declare fields in a tuple or struct using `field name (offset = X, type = T);`, the generated C++ exposes helper wrapper types:
+
+- `rust::FieldOwned<T, OFFSET>` for fields on owning types
+- `rust::FieldRef<T, OFFSET>` for fields on `Ref<Ty>`
+- `rust::FieldRefMut<T, OFFSET>` for fields on `RefMut<Ty>`
+
+These wrappers now act as their underlying type `T` in many contexts:
+
+- `Ref<T>` construction from any `Field*<T, OFFSET>`
+- Implicit read via `operator T()` and `.read()` for value-like access
+- Method calls are forwarded when applicable
+
+Example:
+
+```C++
+rust::Tuple<int32_t, rust::std::string::String> t{42, "hi"_rs.to_owned()};
+
+// Read value
+int32_t v = t.f0; // operator T() on FieldOwned<int32_t, 0>
+
+// Get a Ref<T> from a field
+rust::Ref<int32_t> r = t.f0;
+
+// Access methods through Ref from Field wrappers
+rust::Ref<rust::std::string::String> sref = t.f1;
+auto len = sref.len();
+
+// From references to container, fields become FieldRef/FieldRefMut
+rust::Ref<decltype(t)> rt = t;
+auto l1 = rt.f1.len();
+
+rust::RefMut<decltype(t)> mt = t;
+mt.f1.push_str("!"_rs);
+```
+
+See `examples/regression_test1` for a runnable demonstration.

book/src/call_rust_from_cpp/special_types.md

@@ -17,42 +17,3 @@ tries to support them using C++ feature called User-defined Literals.
 | `'a'_rs_b`     | `b'a'`          | `uint8_t`                         | Not Implemented | unconditionally     |
 | `"hello"_rs_b` | `b"hello"`      | `rust::Ref<rust::Slice<uint8_t>>` | Not Implemented | `[u8]`              |
 | `"hello"_rs_c` | `c"hello"`      | `rust::Ref<rust::ffi::CStr>`      | Not Implemented | `::rust::ffi::CStr` |
-
-## Fields as underlying types
-
-When you declare fields in a tuple or struct using `field name (offset = X, type = T);`, the generated C++ exposes helper wrapper types:
-
-- `rust::FieldOwned<T, OFFSET>` for fields on owning types
-- `rust::FieldRef<T, OFFSET>` for fields on `Ref<Ty>`
-- `rust::FieldRefMut<T, OFFSET>` for fields on `RefMut<Ty>`
-
-These wrappers now act as their underlying type `T` in many contexts:
-
-- `Ref<T>` construction from any `Field*<T, OFFSET>`
-- Implicit read via `operator T()` and `.read()` for value-like access
-- Method calls are forwarded when applicable
-
-Example:
-
-```C++
-rust::Tuple<int32_t, rust::std::string::String> t{42, "hi"_rs.to_owned()};
-
-// Read value
-int32_t v = t.f0; // operator T() on FieldOwned<int32_t, 0>
-
-// Get a Ref<T> from a field
-rust::Ref<int32_t> r = t.f0;
-
-// Access methods through Ref from Field wrappers
-rust::Ref<rust::std::string::String> sref = t.f1;
-auto len = sref.len();
-
-// From references to container, fields become FieldRef/FieldRefMut
-rust::Ref<decltype(t)> rt = t;
-auto l1 = rt.f1.len();
-
-rust::RefMut<decltype(t)> mt = t;
-mt.f1.push_str("!"_rs);
-```
-
-See `examples/regression_test1` for a runnable demonstration.