macros,rust , Can I create a macro that unrolls loops?

Can I create a macro that unrolls loops?


Tag: macros,rust

I'm trying to write some fast matrix code in Rust and to do this needs to ensure that loops are unrolled. Is there a way to create a compile-time for-loop? E.g: I want

unroll_loop!(f, a, 3);

to generate

f(a, 0);
f(a, 1);
f(a, 2);


Well, sort of.

macro_rules! unroll {
    (0, |$i:ident| $s:stmt) => {};
    (1, |$i:ident| $s:stmt) => {{ let $i: usize = 0; $s; }};
    (2, |$i:ident| $s:stmt) => {{ unroll!(1, |$i| $s); let $i: usize = 1; $s; }};
    (3, |$i:ident| $s:stmt) => {{ unroll!(2, |$i| $s); let $i: usize = 2; $s; }};
    (4, |$i:ident| $s:stmt) => {{ unroll!(3, |$i| $s); let $i: usize = 3; $s; }};
    // ...

fn main() {
    unroll!(3, |i| println!("i: {}", i));

You might be tempted to ask "why don't you just use unroll!($i-1, |$i| $s) for the recursive case?". This is because macros cannot do math. In fact, they cannot do any form of evaluation whatsoever. You are basically limited to symbolic manipulation.

Macros also cannot interact with types or values in any way, which means the following does not work, and cannot be made to work:

const N: usize = 3;
unroll!(N, |i| println!("i: {}", i));

So, you can do this, but only for literal integers, and you have to write an explicit case in the macro for every integer to want to be able to use.


How to use multiple variables in routes with Nickel?

Nickel states that you can use variables in the URLs, which sounds very useful, but is it possible to use multiple variables? Something like: server.get("/start/:userid?:passwd", middleware! { |request| // format!("This is user: {:?} = {:?}", // request.param("userid"), // request.param("passwd") // ); }); ...

Load a shared library linked to Rust library in R

Following up on this question here, I am having issues using dyn.load to load a shared library that is linked to a Rust dylib. I suspect it has something to do with where R is looking for the Rust dylib, but I have not found a way to specify another...

Why does Drop take &mut self instead of self?

Why does Drop’s method have signature fn drop(&mut self) instead of fn drop(self)? This makes it difficult to move values out of the fields e.g. self.join_handle.join() or std::mem::drop(self.file) (error: cannot move out of type X, which defines the Drop trait).

Split string in macro

I've a class name with its namespace, like BasicType::MyType. It's possible to create a macro that split the name and uses only the part after the scope operator (I want to create a MyType object in macro without the first part)? EDIT: I'm using a library with different classes in...

Combining multiple template classes to one class using typedef

I have the following piece of code. Let us have the function declaration and implementation seperate. #include <iostream> class Y1 {}; class Y2 {}; template <class T1, class T2> class A { public: explicit A(); void foo() const; int bar() const; }; template <class T1, class T2> A<T1, T2>::A() {}...

Immutable reference after mutable borrow

I've been reading about rust for the past week and (trying) to play around with it. It seems I run into similar problems related to ownership/borrowing every time I use it, so here is the simplest piece of code that sort of illustrates the usual problems. use std::cell::RefCell; struct Res...

Create shared C object linked to Rust dylib for use in R

I am trying to create a shared object I can load into R that calls Rust functions by way of R's C API. To call Rust from C, I am following this blog post. My problem arises when I try to create the shared library and link to the Rust...

Append the string provided by __FUNCTION__ macro

I have defined a macro as following: #define ADD_TIME_ENTRY(_name_) m_pTimeMeasurement->addTimeEntry(_name_); Now, I want to pass the function name through ADD_TIME_ENTRY() in whichsoever function I put ADD_TIME_ENTRY() ADD_TIME_ENTRY(__FUNCTION__) works fine for me but now, I want to add "_start" or "_stop" at the end of the function name. I mean, I...

What is the idiomatic way to write a linked list with a tail pointer?

As a learning project for Rust, I have a very simple (working, if incomplete) implementation of a singly linked list. The declaration of the structs looks like this: type NodePtr<T> = Option<Box<Node<T>>>; struct Node<T> { data: T, next: NodePtr<T>, } pub struct LinkedList<T> { head: NodePtr<T>, } Implementing size and...

Struct vs enum lifetime differences

Why does this work #[derive(Debug)] pub struct Foo<'a,'b> { s : &'a str, n : &'b i32 } #[test] fn test_struct() { let f = Foo { s : &"bar" , n : &17 }; println!("{:?}",f); } but this doesn't #[derive(Debug)] pub enum Bar<'a,'b> { Baz ( &'a str), Fub...

Can I create a macro that unrolls loops?

I'm trying to write some fast matrix code in Rust and to do this needs to ensure that loops are unrolled. Is there a way to create a compile-time for-loop? E.g: I want unroll_loop!(f, a, 3); to generate f(a, 0); f(a, 1); f(a, 2); ...

Return a moving window of elements resulting from an iterator of Vec

I'm trying to figure out how to return a window of elements from a vector that I've first filtered without copying it to a new vector. So this is the naive approach which works fine but I think will end up allocating a new vector from line 5 which I...

Use Weka from ImageJ macro: 'path' is required but unset

I have tried Calling Weka from an ImageJ(Fiji) macro: run("Trainable Weka Segmentation", "open=C:\\input\\test.tif inputfile=C:\input\test.tif path=[Ljava.lang.String;@77e655d8"); But when I run that I get an error message: 'path' is required but unset This line is exactly the line I get when recording a macro and opening test.tif when the Trainable Weka Segmentation...

How can I send a function to another thread?

I am attempting to write a simpler unit test runner for my Rust project. I have created a TestFixture trait that my test fixture structs will implement, similar to inheriting from the unit test base class in other testing frameworks. The trait is fairly simple. This is my test fixture...

How does this code print odd and even?

#define MACRO(num, str) {\ printf("%d", num);\ printf(" is");\ printf(" %s number", str);\ printf("\n");\ } int main(void) { int num; printf("Enter a number: "); scanf("%d", &num); if (num & 1) { MACRO(num, "Odd"); } else { MACRO(num, "Even"); } return 0; } Please explain the above code (if/else condition and how...

How can I create Haskell-like functional dependencies

Background: I'm using the nalgebra library and I want to create a structure that represents a multivariate normal distribution. The number and row type is uniquely determined by a square matrix type, so I want to write something like this: #[allow(non_snake_case)] pub struct Multivar𝒩<M: SquareMat<N, V>> { μ: V, Σ:...

C++ / C #define macro calculation

Suppose I have #define DETUNE1 sqrt(7)-sqrt(5) #define DETUNE2 sqrt(11)-sqrt(7) And I call these multiple times in my program. Are DETUNE1 and DETUNE2 calculated every time it is called? Thanks. Please don't downvote this, I really want to know and a search didn't turn up anything definite. ...

Macro to push arguments onto stack

I've been working on a fun little project to mess around with how functions are called and I need a macro to push arguments as it'll be quite time consuming to push the arguments manually for every instance of this obfuscated call. This is my code so far: #define pushargs(...)...

Implement Debug trait for large array type

I gather that Rust provides Debug impl's for arrays size 32 and smaller. I also gather that I could implement Debug on a larger array by simply using write! with a very long format specifier. But I'm wondering if there's a better way. What is the recommended method for implementing...

Can Rust handle cyclic data structures without any garbage collector?

Is it possible to completely avoid a garbage collector and manual deallocation? Is it possible to implement an interpreter for a language that needs garbage collection (say, Scheme) in Rust, without implementing or using any garbage collector? ...

Cannot infer appropriate lifetime for autoderef in Iterator impl

I am trying to implement the Iterator trait for a struct which basically just acts as a borrower of an array of i32 values. However, I keep running into the compiler complaining about not being able to infer a lifetime inside the next method. I am aware of this answer,...

Unexpected output printf statement [duplicate]

This question already has an answer here: Why is “i” variable getting incremented twice in my program? 8 answers Why outputs of i and j in the following two printf()s are different? #include <cstdio> #define MAX(x,y) (x)>(y)?(x):(y) int main() { int i=10,j=5,k=0; k==MAX(i++,++j); printf("%d %d %d\n",i,j,k); i=10,j=5,k=0; k=MAX(i++,++j); printf("%d...

How to control C Macro Precedence

#define VAL1CHK 20 #define NUM 1 #define JOIN(A,B,C) A##B##C int x = JOIN(VAL,NUM,CHK); With above code my expectation was int x = 20; But i get compilation error as macro expands to int x = VALNUMCHK; // Which is undefined How to make it so that NUM is replaced first...

Create a vector from iterating hashmap

What is the optional way in Rust to iterate a HashMap and collect the result into a Vec? This is my attempt so far: use std::collections::HashMap; struct User { reference: String, email: String } fn main() { let mut users: HashMap<String, User> = HashMap::new(); users.insert("first".to_string(), User { reference: "ref1".to_string(), email:...

Reading immutable value inside spawned thread

I'm trying to make this example work use std::sync::mpsc::{Sender, Receiver}; use std::sync::mpsc; use std::thread; use std::sync::Arc; struct User { reference: String, email: String } struct UserIndex { reference: usize, email: usize } fn main() { let rows = vec![ vec!["abcd", "[email protected]"], vec!["efgh", "[email protected]"], vec!["wfee", "[email protected]"], vec!["rrgr", "[email protected]"] ]; let user_index...

Result has no method called “unwrap()”?

What a strange error: let res1 = get_res(); assert!(res1.is_ok()); assert_eq!("just for test", res1.unwrap()); //error The error is: type `core::result::Result<(MyStruct1, collections::btree::map::BTreeMap<collections::string::String, collections::string::String>), Error>` does not implement any method in scope named `unwrap` ...

Bug in FFI when passing CString followed by an int

My Rust test code extern "C" { fn test_int_only(n : libc::c_int); fn test_int_and_str(s : CString , n : libc::c_int); } pub fn test1() { unsafe { test_int_only(0); test_int_only(1); test_int_only(2); test_int_only(4); test_int_only(-12); } } pub fn test2() { unsafe { test_int_and_str(CString::new("Foo").unwrap(),0); test_int_and_str(CString::new("Bar").unwrap(),1); test_int_and_str(CString::new("Baz").unwrap(),2); test_int_and_str(CString::new("Fub").unwrap(),4); test_int_and_str(CString::new("Bub").unwrap(),-12); } } My C code void...

Lifetime of a mutable element in struct

How can I define a mutable element in a struct? If I have a following example struct User<'a> { reference: String, email: String, addresses: &'a mut Vec<Address> } struct Address { street: String, city: String } fn main() { let mut users = Vec::new(); users.push(User { reference: "ref".to_string(), email: "[email protected]".to_string(),...

Filter vector in place

In Rust is it possible to operate on a vector in-place? I'd like to remove some elements from a Vec, but vec.iter().filter().collect() creates a new vector with borrowed items. I'd like to mutate the original Vec without extra memory allocation (and keep memory of removed elements as an extra capacity...

Value does not live long enough when using multiple threads

This is a simplified example of my situation: use std::sync::mpsc::{Sender, Receiver}; use std::sync::mpsc; use std::thread; struct User { reference: String, email: String } fn main() { let rows = vec![ vec!["abcd", "[email protected]"], vec!["efgh", "[email protected]"], vec!["wfee", "[email protected]"], vec!["rrgr", "[email protected]"] ]; let chunk_len = (rows.len() / 2) as usize; let mut chunks...

What is the most appropriate way to convert nibbles to a u64?

I am trying to learn Rust and decided to write a program that converts a hex string into a u64. Currently, I have parsed the string into a vector of u8 values, each representing four bits (or "nibble"). I wrote the following code to take a Vec<u8> and return a...

the type of this value must be known in this context

I want to get a length of a string which I've split: fn fn1(my_string: String) -> bool { let mut segments = my_string.split("."); if segments.collect().len() == 55 { //...... } // error: the type of this value must be known in this context How can I fix that error?...

Conditionally compile only one module at a time

Sometimes while refactoring a change in one of the modules has impact on every other module (or many others), because say a type has been changed or a function parameter has been changed etc. In this case instead of changing everything and then compiling at once is there a way...

Indexing a String

I want to perform a very simple task, but I cannot manage to stop the compiler from complaining. fn transform(s: String) -> String { let bytes = s.as_bytes(); format!("{}/{}", bytes[0..2], bytes[2..4]) } [u8] does not have a constant size known at compile-time. Some tips making this operation to work as...

How can I open a file with the standard text editor?

My console based program has a config file which can be opened and edited in a text editor. How would I open said config file with the default text editor? I know there is std::process, but I can't get it to work. The program should be able to run on...

Implementing a generic conversion from an object implementing the `Error` trait

I cannot get the following code to compile. I get an error that From is already implemented. If I remove the manual impl of From I get the error that From is not implemented. If I do not implement Error it works fine. I suppose that this is due to...

Why is `Sized` bound necessary in this trait?

I have a simple trait with two associated functions like this: trait WithConstructor : Sized { fn new_with_param(param: usize) -> Self; fn new() -> Self { Self::new_with_param(0) } } The default implementation of the second method (new()) force me to put the Sized bound on the type. Why ? (I...

Pass Python list to Rust function

I have a Rust library that needs to be imported into Python via the ctypes module. My goal is to use Rust functions that take Vec<T> / i32 as arguments and return those types, from Python. Currently, I can pass integers to the Rust functions, and have them return lists...

Why do I need to use self::core::ops?

I'm trying to use Mul from core. This is suggested by the compiler and works: extern crate core; use self::core::ops::Mul; but why doesn't extern crate core; use core::ops::Mul; work? I get the error error: unresolved import `core::ops::Mul`. Did you mean `self::core::ops`?...

Rust: Lifetime of String from file [duplicate]

This question already has an answer here: Return local String as slice 1 answer I'm trying to read in some external GLSL code into Rust. The reading works properly, but I run into a lifetime issue in the final expression (in the Ok(_) branch) error: s does not live...

More convenient way to work with strings in winapi calls

I'm looking for more convenient way to work with std::String in winapi calls in Rust. Using rust v 0.12.0-nigtly with winapi 0.1.22 and user32-sys 0.1.1 Now I'm using something like this: use winapi; use user32; pub fn get_window_title(handle: i32) -> String { let mut v: Vec<u16> = Vec::new(); v.reserve(255); let...

remove duplicates from vector of custom struct

I'm trying to remove duplicates in the below example: struct User { reference: String, email: String } fn main() { let mut users: Vec<User> = Vec::new(); users.push(User { reference: "abc".into(), email: "[email protected]".into() }); users.push(User { reference: "def".into(), email: "[email protected]".into() }); users.push(User { reference: "ghi".into(), email: "[email protected]".into() }); users.sort_by(|a, b|;...

cannot move out of borrowed content - ref doesn't work [duplicate]

This question already has an answer here: “cannot move out of borrowed context” and “use of moved value” 1 answer I have this code: enum MyEnum1 { val1, val2 } struct Struct1 { field1: MyEnum1, field2: String } fn fn1(a: Struct1, b: String, c: String) { let let1 =...

Understanding NASM Macro

I've come around this macro in a assembly source file and I just can't figure out how it's working. So first I come around this function (hevc_deblock.h): cglobal hevc_v_loop_filter_chroma_8, 3, 5, 7, pix, stride, tc, pix0, r3stride sub pixq, 2 lea r3strideq, [3*strideq] mov pix0q, pixq add pixq, r3strideq TRANSPOSE4x8B_LOAD...

Can I create a macro or shortuct for a step of XPath in XQuery?

Do we have Macros in XQuery? If yes, could you please give an example of their usage. I have the following code let $x := //price/ancestor::* Can I someway, using macros or other things write it as follows: let $x := //price/outward So, the outward should mean ancestor::*...

vector method push_all is not found for a custom struct

So in this simple example #![feature(collections)] struct User { reference: String, email: String } fn main() { let rows = vec![ vec!["abcd".to_string(), "[email protected]".to_string()], vec!["efgh".to_string(), "[email protected]".to_string()], vec!["wfee".to_string(), "[email protected]".to_string()], vec!["rrgr".to_string(), "[email protected]".to_string()] ]; let mut rows_mut: Vec<Vec<String>> = Vec::new(); rows_mut.push_all(&rows); let mut users_mut: Vec<User> = Vec::new(); let users = vec![ User { reference:...

Writing Vec to a file

I'm having trouble on writing Vec<u16> content to a file. #[derive(Debug, Copy, Clone, PartialEq)] pub enum ImageFormat { GrayScale, Rgb32, } #[derive(Debug, Copy, Clone, PartialEq)] pub struct ImageHeader { pub width: usize, pub height: usize, pub format: ImageFormat, } pub struct Image { pub header: ImageHeader, pub data: Vec<u16>, }...

Why is my C code printing out an extra line of rows?

#include <stdio.h> #define rows 500 //can define rows as any number int main() { int i,j; for(i=0;i<=rows;++i) { for(j=0;j<(2*i+1);++j) { printf("* "); } printf("\n"); } return 0; } So here is my code, what it does is it prints the number of rows set by #define and creates a right...

“conflicting implementations for trait” when trying to be generic

Background: I'm using the nalgebra library and I want to create a structure that represents a multivariate normal distribution. M is the type of the matrix, e.g. Mat4<f64>. My current attempt looks like this: use std::ops::Mul; use std::marker::PhantomData; use nalgebra::*; #[allow(non_snake_case)] pub struct Multivar𝒩<N, V, M: SquareMat<N, V>> { μ:...