Questions tagged [rust-decl-macros]
28 questions
86
votes
4 answers
How do I see the expanded macro code that's causing my compile error?
I have a compile error involving a macro:
:6:19: 6:50 error: cannot move out of captured outer variable in an `FnMut` closure
:6 bind ( $ e , move | $ p | mdo ! { $ ( $ t ) * } ) ) ; (
…
Caspar
- 7,039
- 4
- 29
- 41
13
votes
1 answer
What does an @ symbol mean in a Rust declarative macro?
I have seen the @ symbol used in macros but I cannot find mention of it in the Rust Book or in any official documentation or blog posts. For example, in this Stack Overflow answer it is used like this:
macro_rules! instructions {
(enum…
Peter Hall
- 53,120
- 14
- 139
- 204
12
votes
1 answer
Import macro from parent module
I'm having trouble re-using macros within a crate.
If a macro is defined in ./src/macros.rs:
#[macro_export]
macro_rules! my_macro {
...
}
and used in ./src/lib.rs:
#[macro_use]
pub mod macros;
I can't see this macro in…
marcusklaas
- 492
- 5
- 15
7
votes
1 answer
Build all pairs of elements (quadratic set) in declarative macro
I have a list of identifier and I want to invoke a macro for each pair of identifiers from that list. For example, if I have a, b and c, I would like to generate this:
println!("{} <-> {}", a, a);
println!("{} <-> {}", a, b);
println!("{} <-> {}",…
Lukas Kalbertodt
- 79,749
- 26
- 255
- 305
6
votes
0 answers
How to make a macro expand before stringifying it in Rust?
I'm trying to write a quine in Rust using only macros.
In order to do that, I'm embedding the main function into macro f1, and trying to embed a literal representation of f1 in f2 with stringify!.
Here is my code so far:
macro_rules!f1{()=>(fn…
Jon Nimrod
- 335
- 1
- 2
- 12
6
votes
1 answer
Pass entire macro input to another macro
I'm trying to make a simple macro that invokes vec! with whatever it receives then does some simple processing before returning the new vector:
macro_rules! sorted_vec {
($x:expr) => {
{
let v = vec![$x];
…
anderspitman
- 9,230
- 10
- 40
- 61
5
votes
2 answers
How can I generate trait bounds in a declarative macro?
I have a trait with a large number of associated types. I want a function that uses those associated types on both sides of a where clause bound:
trait Kind {
type A;
type B;
// 20+ more types
}
trait Bound {}
fn example
Shepmaster
- 388,571
- 95
- 1,107
- 1,366
5
votes
1 answer
How to write a macro that displays the file and line number and a variable number of arguments?
I've found several useful macros in Rust, namely: file!(), line!(), stringify!() I've also found that Rust allows macros with variable arguments, as stated here:
macro_rules! print_all {
($($args:expr),*) => {{
$(
…
Wakan Tanka
- 7,542
- 16
- 69
- 122
4
votes
1 answer
How to return a new String from a declarative macro?
So here I am, trucking along with Rustlings, until I get broadsided with test 4.
It wants me to write a macro that will satisfy the following code:
fn main() {
if my_macro!("world!") != "Hello world!" {
panic!("Oh no! Wrong output!");
…
AerosolSP
- 177
- 1
- 1
- 10
3
votes
1 answer
How to parse single tokens in rust macros
I'm starting playing with Rust macros and I came to try this little practice example. I want to define a macro that expands into a variable initialization (name doesn't matter) of type i32 (for example, but not really important) and a series of…
Netwave
- 40,134
- 6
- 50
- 93
2
votes
1 answer
How do I detect if an optional keyword was supplied to a declarative macro?
I'm writing a macro:
macro_rules! foo {
($(print)?) => {
// run `println!("hello") if print is given
}
}
Which could be called as:
foo!() which would do nothing
foo!(print) which would print hello
How do I detect if print was…
lolad
- 321
- 6
- 13
2
votes
1 answer
How to match a trait in a Rust macro?
My goal is to take as input trait type.
my_test_macro!(Trait1, Trait2)
What I tried so far was writing parser like this.
$( $ty:ident < $( $N:ident $(: $b0:ident $(+$b:ident)* )? ),* $($tname:ident=$ttype:ident),* > )+*
But it…
Inline
- 2,566
- 1
- 16
- 32
1
vote
2 answers
How do I early return in declarative macros and infer the return type?
I have a macro, which just generates an instance of a struct, as below:
macro_rules! foo {
() => {{
let baz_val = baz();
let bar_val = match bar() {
Ok(val) => val,
Err(err) => {
…
Eray Erdin
- 2,633
- 1
- 32
- 66
1
vote
1 answer
How do I generate a macro from previous macro-generated code?
In order to create a pyo3-powered Python class working with a struct that uses generic type, I want to use wrappers that will generate the code needed to not have to do it for every specific type.
I created a macro that generates the code but I need…
litchipi
- 53
- 1
- 5
1
vote
2 answers
How do I get an identifer from an expression argument in a macro?
I have a constant value defined by a variable:
const VAL: usize = 32;
I want to make a function like this:
macro_rules! valfn {
($val:expr) => {
pub fn $val () -> () { // here val needs to be a ident
some_other_fn($val) …
user318904
- 2,968
- 4
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- 37