Change the parameter name of From::from to value

[ghost]

The From trait is currently defined as:

pub trait From<T>: Sized {
    fn from(_: T) -> Self;
}

The name of the argument is _. I am proposing to change it to value, ie.

pub trait From<T>: Sized {
    fn from(value: T) -> Self;
}

This would be more consistent with the TryFrom, which looks like this:

pub trait TryFrom<T>: Sized {
    type Error;
    fn try_from(value: T) -> Result<Self, Self::Error>;
}

The reason for this proposal is twofold:

1. Consistency with the rest of the standard library. The TryFrom trait uses value, and no From implementation uses the default name (as it is quite useless).
2. When generating trait implementations with rust-analyzer/IntelliJ, the parameter name is copied, and it always has to be changed.

Optionally, another name like x could be used. I only propose value for consistency with TryFrom.

Changing parameter names is not a breaking change.

Note: this was originally posted as an internals thread here

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @scottmcm (or someone else) soon.

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[scottmcm]

Thanks for the PR! This makes good sense to me. It was probably only this way because it's a super-old trait and way back when it was possible to write trait From<T> { fn from(T) -> Self; } without an argument name at all, and everything was auto-migrated. Matching TryFrom (a newer trait!) is a good solution.

@bors r+ rollup=always

[bors]

📌 Commit 8dcecdb has been approved by scottmcm

It is now in the queue for this repository.