Split ToVariant and FromVariant traits #187
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This allows types to be separately `ToVariant` and `FromVariant`, enabling `ToVariant`-only types to be returned by exported methods, or the other way around. Also relaxes the `Sized` bound on `ToVariant`, so it can be made into trait objects, and passed across threads in boxes.
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karroffel
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Aug 29, 2019
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Cherry-picked this off #181 because I think it would still be useful out of that PR's context, and can be reviewed individually, for use cases like #185 (comment), where you only really need a one-way conversion.
Related sections from the original PR comment:
Explanation
This allows types to be separately
ToVariantandFromVariant.ToVariantno longer requireSized. Bounds on export function arguments, return values, and property getter / setters are relaxed to require only one of these traits. As such, it's now possible to:FromVariantas an argument. e.g. a custom "options" struct that reads from aDictionary.ToVariantas a return value. e.g.Instance<T>.ToVarianttypes into trait objects and send them through Rust channels:Box<dyn ToVariant + Send + 'static>.All types that previously implement
ToVariantare now alsoFromVariant.Drawbacks
ToVariantimplementations on custom types are void, although a fix is very easy.ToVariantas a bound and callfrom_variantneed to do useFromVariant(orToVariant + FromVariant) instead.