Generated constructor code calls NewUnionNull*() which is overwritten by nil

[i7tsov]

I've noticed some weirdness in the generated code:

func NewSample() Sample {
    r := Sample{}
    r.Number = 0
    r.NestedArray = NewUnionNullArrayNested()

    r.NestedArray = nil
    r.Mapping = NewUnionNullMapString()

    r.Mapping = nil
    return r
}

Avro schema contains unions of null&array and null&map. The result of NewUnionNullArrayNested() is instantly overwritten with nil (which is the default value for the field), allocating unnecessary memory on the heap. As far as I can see, there are no side effects of NewUnionNullArrayNested() function.

func NewUnionNullArrayNested() *UnionNullArrayNested {
    return &UnionNullArrayNested{}
}

Is that intended?

[actgardner]

Hey @i7tsov, can you post the Avro schema that produces this code?

[i7tsov]

Sure.

{
  "type": "record",
  "name": "Sample",
  "namespace": "foo",
  "fields": [
    {
      "name": "number",
      "type": "int",
      "default": 0
    },
    {
      "name": "nestedArray",
      "type": [
        "null",
        {
          "type": "array",
          "items": {
            "type": "record",
            "name": "nested",
            "fields": [
              {
                "name": "name",
                "type": "string",
                "default": ""
              },
              {
                "name": "count",
                "type": "int",
                "default": 0
              }
            ]
          }
        }
      ],
      "default": null
    },
    {
      "name": "mapping",
      "type": [
        "null",
        {
          "type": "map",
          "values": "string"
        }
      ],
      "default": null
    }
  ]
}

The root cause here from my understanding is that the field is a union of null and array (or map), and the default value is null. But generated code can be optimized to not create the instance of values other than null in such case.

[actgardner]

@i7tsov I've fixed this so that when the union field's default is null, the record constructor skips instantiating the struct.