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Support nested Attribute values (#376) #596

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Support nested Attribute values (#376) #596

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Support nested Attribute values (#376)
shengxil May 12, 2020
d1f9092
Only allow children attributes array
shengxil May 14, 2020
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5 changes: 3 additions & 2 deletions specification/trace/api.md
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Expand Up @@ -376,8 +376,9 @@ An `Attribute` is defined by the following properties:
- (Required) The attribute key, which MUST be a non-`null` and non-empty string.
- (Required) The attribute value, which is either:
- A primitive type: string, boolean or numeric.
- An array of primitive type values. The array MUST be homogeneous,
i.e. it MUST NOT contain values of different types.
- A child Attribute
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@Oberon00 Oberon00 May 12, 2020 •
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A single child attribute? That does not sound useful. So instead of Attribute(3), I could have Attribute(Attribute(Attribute(3)))? That's probably not what you meant to say.

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Ah, I think I understand: The attribute does include the key! Then I would allow the child attribute only in the array because Attribute(key=foo, value=Attribute(key=bar, value=42)) sounds useless.

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@shengxil shengxil May 14, 2020 •
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Appreciate the feedback! Yeah that makes sense. Even if some use cases need a single child attribute, it can still be placed in the array. I'll updating the PR.

- An array of primitive type values or children Attributes. The array MUST be
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The array restrictions (no nested arrays, no different types) were made to ease implementation and APIs in statically typed languages. This PR would mostly negate this, because by using an array of attributes you could have different values inside these attributes, including arrays.

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I would argue that the current homogeneous convention is made because some languages can't accept array with different member types. If we consider the whole Attribute as a firm type, and consider its value type and value as its property, then within an array all sibling Attribute are still the same type.

Programming-wise IMHO, Attribute encapsulates the data so from the array's point of view, the value type is invisible.

homogeneous, i.e. it MUST NOT contain values of different types.

The Span interface MUST provide:

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