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Add index getter to Variant #110

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Jul 9, 2021
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Add index getter to Variant #110

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8025135
Add index getter to Variant
ascjones Jul 9, 2021
9857899
Update comment.
ascjones Jul 9, 2021
e6f160f
Update release notes and CHANGELOG
ascjones Jul 9, 2021
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6 changes: 6 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,7 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

## [0.9.2] - 2021-07-09
### Added

- Add index getter to Variant [(#110)](https://github.com/paritytech/scale-info/pull/110)

## [0.9.1] - 2021-07-06
### Fixed

- Option constructor macro hygiene [(#108)](https://github.com/paritytech/scale-info/pull/108)

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2 changes: 1 addition & 1 deletion Cargo.toml
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@@ -1,6 +1,6 @@
[package]
name = "scale-info"
version = "0.9.1"
version = "0.9.2"
authors = ["Parity Technologies <[email protected]>"]
edition = "2018"

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5 changes: 5 additions & 0 deletions src/ty/variant.rs
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Expand Up @@ -230,6 +230,11 @@ where
&self.fields
}

/// Returns the index of the variant, if specified.
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👍

pub fn index(&self) -> Option<u8> {
self.index
}
Comment on lines +233 to +236
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What is the difference here from the discriminant?

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The discriminant is only valid for "C Like" enums.

If both are specified then the index takes precedence for encoding. We still retain the discriminant though for e.g. reconstructing the original type.

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Ah okay I see. Although we should keep in mind that there is a Rust RFC to allow for discriminants for data variants. Although then #[scale(index = N)] would still override those which should be fine.

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Yes that would still hold true. You are correct that index specifically refers to the value from the attribute. And it can be different from the discriminator, but will take precedence for encoding.

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keep in mind that there is a Rust RFC

If/when that lands and is stabilised we could deprecate the #[scale(index = N)] attribute and only use discriminants. That would be nice (and a breaking change both to us and parity-scale-codec).

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Discriminant removed in #112


/// Returns the discriminant of the variant.
pub fn discriminant(&self) -> Option<u64> {
self.discriminant
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