[rust-dev] Can macro use variable values?

[Daneel Yaitskov]

Hi,


Does Rust macro have flow control based on a variable value?

I didn't find such info here http://doc.rust-lang.org/guide-macros.html.

I'd like to get a macro expading a for loop.

doTimes(3, println!("DDDD"))
=>
println!("DDDD")
println!("DDDD")
println!("DDDD")

[John Clements]

Post by Daneel Yaitskov
Hi,
Does Rust macro have flow control based on a variable value?
I didn't find such info here http://doc.rust-lang.org/guide-macros.html.
I'd like to get a macro expading a for loop.
doTimes(3, println!("DDDD"))
=>
println!("DDDD")
println!("DDDD")
println!("DDDD?)

Perhaps I?m misunderstanding you, but in general that?s impossible. Specifically, variable varues aren?t known at runtime. So, for instance, if you wrote

doTimes(x, println!(?DDDD?))

? there?s no way (in general) to know the value of ?x? until the program is run.

Is there some reason you can?t just use a function call, here?

John Clements

[Evan G]

The thought is that you should be able to do it with static variables
(ones that are known at compile time, like his example)

This is known as Compile Time Function Evaluation, I know there's been
some work on it, and you can probably search the RFCs to figure out
the status currently.

On Wed, Sep 24, 2014 at 11:30 AM, John Clements

Post by John Clements

Post by Daneel Yaitskov
Hi,
Does Rust macro have flow control based on a variable value?
I didn't find such info here http://doc.rust-lang.org/guide-macros.html.
I'd like to get a macro expading a for loop.
doTimes(3, println!("DDDD"))
=>
println!("DDDD")
println!("DDDD")
println!("DDDD?)

doTimes(x, println!(?DDDD?))
? there?s no way (in general) to know the value of ?x? until the program is run.
Is there some reason you can?t just use a function call, here?
John Clements
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