Since Rust 1.34, you can use extern crate self as my_crate, and use my_crate::Foo instead of $crate::Foo. https://github.com/rust-lang/rust/issues/54647 https://github.com/rust-lang/rust/pull/57407 (Credit: Neptunepink ##rust irc.freenode.net)
Rust macros aren’t able to do that. Macros operate at the syntactic level, not at the semantic level. That means that although the compiler knows it has an expression (syntax), it doesn’t know what the type of the expression’s value (semantic) is at the moment the macro is expanded. A workaround would be to pass … Read more
Yes however this is only available as a nightly-only experimental API which may be removed. You can pass arbitrary identifier into a macro and yes, you can concatenate identifiers into a new identifier using concat_idents!() macro: #![feature(concat_idents)] macro_rules! test { ($x:ident) => ({ let z = concat_idents!(hello_, $x); z(); }) } fn hello_world() { } … Read more
There is now a generalized threading macro in Clojure since 1.5 called as->. This tweet gives an example of how it works: https://twitter.com/borkdude/status/302881431649128448 (as-> “/tmp” x (java.io.File. x) (file-seq x) (filter (memfn isDirectory) x) (count x)) First ‘x’ is bound to “/tmp” and a file is made out of it. ‘x’ is rebound again to … Read more
One way to do this is to assign your key sequence to a macro, then run the macro once followed by the @@ run-last-macro command. For example: qa.jq@a@@ If you know how many times you want to repeat the macro, you can use 4@@ or whatever.
These are pretty tricky constructs, and it’s tough to give clear explanations; they aren’t as straightforward as Lisp macros (or, for that matter, the relationship between Lisp’s QUOTE and EVAL). However, there’s a good, lengthy discussion available in the form of notes from Robby Villegas’s 1999 talk “Unevaluated Expressions” on Wolfram’s website. Defer is omitted … Read more
That’s a notion introduced to ensure that whatever is in a macro invocation correctly matches (), [] and {} pairs. tt will match any single token or any pair of parenthesis/brackets/braces with their content. For example, for the following program: fn main() { println!(“Hello world!”); } The token trees would be: fn main () ∅ … Read more
Source code transformations. All kinds. Examples: New control flow statements: You need a WHILE statement? Your language doesn’t have one? Why wait for the benevolent dictator to maybe add one next year. Write it yourself. In five minutes. Shorter code: You need twenty class declarations that almost look identical – only a limited amount of … Read more
Replacement only occurrs for a function-like macro if the macro name is followed by a left parenthesis. So, the following all invoke the function-like macro MY_MACRO(): MY_MACRO() MY_MACRO ( ) MY_MACRO ( ) But this would not: MY_MACRO SomethingElse It depends on how you are using the macro and what it is used for as … Read more
Currently this is not supported in stable. However there is a feature in nightly called concat_idents: concat_idents!(my_test_, $id) See Rust docs Issue Update: it seems there aren’t near-term plans to add this into stable releases, see issue.