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Add index getter to Variant #110

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Merged
ascjones merged 3 commits into from
Jul 9, 2021
Merged

Add index getter to Variant #110

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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 <admin@parity.io>"]
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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@dvdplm dvdplm Jul 14, 2021

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👍

pub fn index(&self) -> Option<u8> {
self.index
}
Comment on lines +233 to +236
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@Robbepop Robbepop Jul 9, 2021

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What is the difference here from the discriminant?

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@ascjones ascjones Jul 9, 2021

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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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@Robbepop Robbepop Jul 9, 2021

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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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@ascjones ascjones Jul 9, 2021

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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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@dvdplm dvdplm Jul 14, 2021

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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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@ascjones ascjones Jul 15, 2021

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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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