resolve comments: update rust comments

Author: xieyuschen

iceoryx2/src/service/static_config/message_type_details.rs

@@ -20,10 +20,24 @@ use serde::{Deserialize, Serialize};
 #[derive(Default, Debug, Clone, Eq, Hash, PartialEq, Serialize, Deserialize)]
 pub enum TypeVariant {
     #[default]
-    /// A fixed size type which is determined during compile.
-    /// A structure holds some pointer fields should be clarified as Dynamic.
+    /// A type notated by [`#[repr(C)]`](https://doc.rust-lang.org/reference/type-layout.html#reprc).
+    /// with a constant size known at compile time is recognized as FixedSize.
+    /// The FixedSize type should satisfy the [`Sized`].
+    /// For example, all primitive types are FixedSize. The self-contained structs(without pointer members
+    /// or heap-usages) are FixedSize.
     FixedSize,
-    /// A dynamic sized type like a slice or it contains some pointer fields.
+
+    /// A dynamic sized type strictly refers to the slice of an iceoryx2 compatible types.
+    /// The struct with pointer members or with heap usage MUSTN't be recognized as Dynamic type.
+    /// Indeed, they're the in-compatible iceoryx2 types.
+    ///
+    /// The underlying reason is the shared memory which we use to store the payload data.
+    /// If the payload type would use the heap then the type would use
+    /// process local memory that is not available to another process.
+    ///
+    /// The pointer requirement comes again from shared memory.
+    /// It has a different pointer address offset in every process rendering any absolute pointer
+    /// useless and dereferencing it would end up in a segfault.
     Dynamic,
 }
 
@@ -37,6 +51,7 @@ pub struct TypeDetail {
     /// The size of the underlying type calculated by [`core::mem::size_of`].
     pub size: usize,
     /// The ABI-required minimum alignment of the underlying type calculated by [`core::mem::align_of`].
+    /// It may be set by users with a larger alignment, e.g the memory provided by allocator used by SIMD.
     pub alignment: usize,
 }
 
@@ -79,7 +94,7 @@ impl MessageTypeDetails {
         payload_start as *const u8
     }
 
-    /// returns pointer of user_header which is the field follows the header field in a structure.
+    /// returns the pointer to the user header
     pub(crate) fn user_header_ptr_from_header(&self, header: *const u8) -> *const u8 {
         let header = header as usize;
         let user_header_start = align(header + self.header.size, self.user_header.alignment);
@@ -136,7 +151,7 @@ mod tests {
             _b: bool,
             _c: i64,
         }
-        
+
         let sut = MessageTypeDetails::from::<i32, i64, MyPayload>(TypeVariant::FixedSize);
         let expected = MessageTypeDetails{
             header:  TypeDetail{