io::Error::new(_, string literal) allocates Box<Box<String>> and copies the string #83352
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m-ou-se
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T-libs
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I think this is a duplicate of #82812 (or vice versa). |
Dylan-DPC-zz
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Mar 23, 2021
Add internal io::Error::new_const to avoid allocations. This makes it possible to have a io::Error containing a message with zero allocations, and uses that everywhere to avoid the *three* allocations involved in `io::Error::new(kind, "message")`. The function signature isn't perfect, because it needs a reference to the `&str`. So for now, this is just a `pub(crate)` function. Later, we'll be able to use `fn new_const<MSG: &'static str>(kind: ErrorKind)` to make that a bit better. (Then we'll also be able to use some ZST trickery if that would result in more efficient code.) See rust-lang#83352
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this issue
Mar 23, 2021
Add internal io::Error::new_const to avoid allocations. This makes it possible to have a io::Error containing a message with zero allocations, and uses that everywhere to avoid the *three* allocations involved in `io::Error::new(kind, "message")`. The function signature isn't perfect, because it needs a reference to the `&str`. So for now, this is just a `pub(crate)` function. Later, we'll be able to use `fn new_const<MSG: &'static str>(kind: ErrorKind)` to make that a bit better. (Then we'll also be able to use some ZST trickery if that would result in more efficient code.) See rust-lang#83352
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this issue
Mar 24, 2021
Add internal io::Error::new_const to avoid allocations. This makes it possible to have a io::Error containing a message with zero allocations, and uses that everywhere to avoid the *three* allocations involved in `io::Error::new(kind, "message")`. The function signature isn't perfect, because it needs a reference to the `&str`. So for now, this is just a `pub(crate)` function. Later, we'll be able to use `fn new_const<MSG: &'static str>(kind: ErrorKind)` to make that a bit better. (Then we'll also be able to use some ZST trickery if that would result in more efficient code.) See rust-lang#83352
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Should we consider providing a stable |
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It'd have to be |
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It's very common to use
io::Error::new(kind, "some message"), including in many places instd. However, that will create aio::Errorcontaining aRepr::Customcontaining aBox<Custom>containing aBox<dyn Error + ..>containing aStringErrorcontaining aStringcontaining a copy of the message. 🙃Three allocations to just return an error message which is in some cases not even more helpful than just the ErrorKind, is not great. We should find a way to improve this.
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