Macro size_of_field 

macro_rules! size_of_field {
    ($type_name:ty, $($field:ident).+) => { ... };
}

Get the size of a field in a struct.

This is a compile-time equivalent of std::mem::size_of_val(&value.field).

Usage:

struct MyStruct {
    field1: u8,
    nested: Nested,
}

struct Nested {
    field2: u32,
}

const FIELD1_SIZE: usize = size_of_field!(MyStruct, field1);
const FIELD2_SIZE: usize = size_of_field!(MyStruct, nested.field2);