diff options
Diffstat (limited to 'quote/README.md')
| -rw-r--r-- | quote/README.md | 237 |
1 files changed, 0 insertions, 237 deletions
diff --git a/quote/README.md b/quote/README.md deleted file mode 100644 index 7c7f743..0000000 --- a/quote/README.md +++ /dev/null @@ -1,237 +0,0 @@ -Rust Quasi-Quoting -================== - -[](https://travis-ci.org/dtolnay/quote) -[](https://crates.io/crates/quote) -[](https://docs.rs/quote/) - -This crate provides the [`quote!`] macro for turning Rust syntax tree data -structures into tokens of source code. - -[`quote!`]: https://docs.rs/quote/1.0/quote/macro.quote.html - -Procedural macros in Rust receive a stream of tokens as input, execute arbitrary -Rust code to determine how to manipulate those tokens, and produce a stream of -tokens to hand back to the compiler to compile into the caller's crate. -Quasi-quoting is a solution to one piece of that — producing tokens to -return to the compiler. - -The idea of quasi-quoting is that we write *code* that we treat as *data*. -Within the `quote!` macro, we can write what looks like code to our text editor -or IDE. We get all the benefits of the editor's brace matching, syntax -highlighting, indentation, and maybe autocompletion. But rather than compiling -that as code into the current crate, we can treat it as data, pass it around, -mutate it, and eventually hand it back to the compiler as tokens to compile into -the macro caller's crate. - -This crate is motivated by the procedural macro use case, but is a -general-purpose Rust quasi-quoting library and is not specific to procedural -macros. - -*Version requirement: Quote supports any compiler version back to Rust's very -first support for procedural macros in Rust 1.15.0.* - -[*Release notes*](https://github.com/dtolnay/quote/releases) - -```toml -[dependencies] -quote = "1.0" -``` - -## Syntax - -The quote crate provides a [`quote!`] macro within which you can write Rust code -that gets packaged into a [`TokenStream`] and can be treated as data. You should -think of `TokenStream` as representing a fragment of Rust source code. - -[`TokenStream`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.TokenStream.html - -Within the `quote!` macro, interpolation is done with `#var`. Any type -implementing the [`quote::ToTokens`] trait can be interpolated. This includes -most Rust primitive types as well as most of the syntax tree types from [`syn`]. - -[`quote::ToTokens`]: https://docs.rs/quote/1.0/quote/trait.ToTokens.html -[`syn`]: https://github.com/dtolnay/syn - -```rust -let tokens = quote! { - struct SerializeWith #generics #where_clause { - value: &'a #field_ty, - phantom: core::marker::PhantomData<#item_ty>, - } - - impl #generics serde::Serialize for SerializeWith #generics #where_clause { - fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> - where - S: serde::Serializer, - { - #path(self.value, serializer) - } - } - - SerializeWith { - value: #value, - phantom: core::marker::PhantomData::<#item_ty>, - } -}; -``` - -## Repetition - -Repetition is done using `#(...)*` or `#(...),*` similar to `macro_rules!`. This -iterates through the elements of any variable interpolated within the repetition -and inserts a copy of the repetition body for each one. The variables in an -interpolation may be anything that implements `IntoIterator`, including `Vec` or -a pre-existing iterator. - -- `#(#var)*` — no separators -- `#(#var),*` — the character before the asterisk is used as a separator -- `#( struct #var; )*` — the repetition can contain other things -- `#( #k => println!("{}", #v), )*` — even multiple interpolations - -Note that there is a difference between `#(#var ,)*` and `#(#var),*`—the latter -does not produce a trailing comma. This matches the behavior of delimiters in -`macro_rules!`. - -## Returning tokens to the compiler - -The `quote!` macro evaluates to an expression of type -`proc_macro2::TokenStream`. Meanwhile Rust procedural macros are expected to -return the type `proc_macro::TokenStream`. - -The difference between the two types is that `proc_macro` types are entirely -specific to procedural macros and cannot ever exist in code outside of a -procedural macro, while `proc_macro2` types may exist anywhere including tests -and non-macro code like main.rs and build.rs. This is why even the procedural -macro ecosystem is largely built around `proc_macro2`, because that ensures the -libraries are unit testable and accessible in non-macro contexts. - -There is a [`From`]-conversion in both directions so returning the output of -`quote!` from a procedural macro usually looks like `tokens.into()` or -`proc_macro::TokenStream::from(tokens)`. - -[`From`]: https://doc.rust-lang.org/std/convert/trait.From.html - -## Examples - -### Combining quoted fragments - -Usually you don't end up constructing an entire final `TokenStream` in one -piece. Different parts may come from different helper functions. The tokens -produced by `quote!` themselves implement `ToTokens` and so can be interpolated -into later `quote!` invocations to build up a final result. - -```rust -let type_definition = quote! {...}; -let methods = quote! {...}; - -let tokens = quote! { - #type_definition - #methods -}; -``` - -### Constructing identifiers - -Suppose we have an identifier `ident` which came from somewhere in a macro -input and we need to modify it in some way for the macro output. Let's consider -prepending the identifier with an underscore. - -Simply interpolating the identifier next to an underscore will not have the -behavior of concatenating them. The underscore and the identifier will continue -to be two separate tokens as if you had written `_ x`. - -```rust -// incorrect -quote! { - let mut _#ident = 0; -} -``` - -The solution is to build a new identifier token with the correct value. As this -is such a common case, the `format_ident!` macro provides a convenient utility -for doing so correctly. - -```rust -let varname = format_ident!("_{}", ident); -quote! { - let mut #varname = 0; -} -``` - -Alternatively, the APIs provided by Syn and proc-macro2 can be used to directly -build the identifier. This is roughly equivalent to the above, but will not -handle `ident` being a raw identifier. - -```rust -let concatenated = format!("_{}", ident); -let varname = syn::Ident::new(&concatenated, ident.span()); -quote! { - let mut #varname = 0; -} -``` - -### Making method calls - -Let's say our macro requires some type specified in the macro input to have a -constructor called `new`. We have the type in a variable called `field_type` of -type `syn::Type` and want to invoke the constructor. - -```rust -// incorrect -quote! { - let value = #field_type::new(); -} -``` - -This works only sometimes. If `field_type` is `String`, the expanded code -contains `String::new()` which is fine. But if `field_type` is something like -`Vec<i32>` then the expanded code is `Vec<i32>::new()` which is invalid syntax. -Ordinarily in handwritten Rust we would write `Vec::<i32>::new()` but for macros -often the following is more convenient. - -```rust -quote! { - let value = <#field_type>::new(); -} -``` - -This expands to `<Vec<i32>>::new()` which behaves correctly. - -A similar pattern is appropriate for trait methods. - -```rust -quote! { - let value = <#field_type as core::default::Default>::default(); -} -``` - -## Hygiene - -Any interpolated tokens preserve the `Span` information provided by their -`ToTokens` implementation. Tokens that originate within a `quote!` invocation -are spanned with [`Span::call_site()`]. - -[`Span::call_site()`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html#method.call_site - -A different span can be provided explicitly through the [`quote_spanned!`] -macro. - -[`quote_spanned!`]: https://docs.rs/quote/1.0/quote/macro.quote_spanned.html - -<br> - -#### License - -<sup> -Licensed under either of <a href="LICENSE-APACHE">Apache License, Version -2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option. -</sup> - -<br> - -<sub> -Unless you explicitly state otherwise, any contribution intentionally submitted -for inclusion in this crate by you, as defined in the Apache-2.0 license, shall -be dual licensed as above, without any additional terms or conditions. -</sub> |