ParseAndPackDecoder

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title: ParseAndPackDecoder
---

# Strategy

*   P-trie in code, top-down parsing 
*   Message storage allocated from pool 
*   Bottom-up packaging

## Example

struct BASE_MSG {
        enum MSG_TYPE type;
        size_t size;
    };
    
    struct PARENT_MSG {
        struct BASE_MSG base;
        enum PARENT_MSG_TYPE type;
        int pdata1;
    };
    
    struct CHILD_MSG {
        struct PARENT_MSG parent;
        int cdata1;
        int cdata2;
    };

# Pro

*   Easy to initialise 
        CHILD_MSG cm = {
            {
                {
                    MSG_TYPE_PARENT, // contains PARENT_MSG
                    sizeof(CHILD_MSG)
                }, // BASE_MSG
                PARENT_MSG_TYPE_CHILD, // contains CHILD_MSG
                parent_data1
            }, //PARENT_MSG
            child_data1,
            child_data2
        }; // CHILD_MSG

# Con

*   Member access looks a bit messy 
*   Bottom-up access is counter-intuitive 
        cm.parent.pdata1 = parent_data1;
        cm.parent.pdata2 = parent_data2;

*   Can only be used for fixed-size message hierarchies

# Notes

*   Either use global type for all messages (used in BASE_MSG and inherited) 
*   Or hierarchical type member (present in each sub-message) 
*   Global size for passing around safely 
*   Or hierarchical types

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