[jira] [Commented] (AVRO-1994) C++ Code Generator Generates Invalid Code if Field is of type Null

["Darryl Green (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AVRO-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15863296#comment-15863296 ] 

Darryl Green commented on AVRO-1994:
------------------------------------

Thanks for the fast turn-around on this issue.

One question/comment on the patch:

I did make a change that seemed to fix the problem locally with:

{code}
#include "boost/blank"
namespace avro {
typedef boost::blank null;
}
{code}

And the obvious/mechanical changes to generator and codec_traits to support this type.

{code}
template <> struct codec_traits<avro::null> {
	/**
	* Encodes a given value.
	*/
	static void encode(Encoder& e, const avro::null&) {
		e.encodeNull();
	}

	/**
	* Decodes into a given value.
	*/
	static void decode(Decoder& d, avro::null&) {
		d.decodeNull();
	}
};

{code}

and 

{code}
string CodeGen::cppTypeOf(const NodePtr& n)
{
   switch (n->type()) {
 ...
    case avro::AVRO_NULL:
        return "avro::null";
    default:
        return "$Undefined$";
    }
}
{code}


The only reason I mention this is that it plays nicely with/is consistent with changes to use boost::variant (which can use boost::blank to represent "empty" state of a union) to represent Avro unions and support visitation. While there may be advantages in avoiding having a null value take up space (even struct{} has a non-zero size) there are also advantages in a null field "existing" like any other.

Note I haven't proposed a variant patch yet because what I have breaks recursive type support and I can't see a way out of that without it becoming a change that doesn't actually address the problems I had hoped to fix.


> C++ Code Generator Generates Invalid Code if Field is of type Null
> ------------------------------------------------------------------
>
>                 Key: AVRO-1994
>                 URL: https://issues.apache.org/jira/browse/AVRO-1994
>             Project: Avro
>          Issue Type: Bug
>          Components: c++
>            Reporter: Darryl Green
>         Attachments: AVRO-1994.patch
>
>
> An simple schema like this:
> {
>         "name": "TestPrimitiveTypes",
>         "type": "record",
>         "fields": [
>             { "name": "Null", "type": "null" },
>             { "name": "Boolean", "type": "boolean" },
>             { "name": "Int", "type": "int" },
>             { "name": "Long", "type": "long" },
>             { "name": "Float", "type": "float" },
>             { "name": "Double", "type": "double" },
>             { "name": "Bytes", "type": "bytes" },
>             { "name": "String", "type": "string" }
>         ]
>     }
> Generates this C++ struct.
> struct TestPrimitiveTypes {
>     $Undefined$ Null; // <-- BUG!
>     bool Boolean;
>     int32_t Int;
>     int64_t Long;
>     float Float;
>     double Double;
>     std::vector<uint8_t> Bytes;
>     std::string String;
>     TestPrimitiveTypes() :
>         Null($Undefined$()),
>         Boolean(bool()),
>         Int(int32_t()),
>         Long(int64_t()),
>         Float(float()),
>         Double(double()),
>         Bytes(std::vector<uint8_t>()),
>         String(std::string())
>         { }
> };
> Note the C++ type of the field Null is $Undefined$ which is obviously invalid/won't compile. 



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