CODEWITHSUNDEEP
rust
wonderflow
wonderflow

Reputation: 755

Why my const variable can't be found in different mod

I define a const variable in main.rs and want to use it in different file.

in src/main.rs, I define such const, no matter and pub or not, it didn’t use:

const CONFIG_GROUP: &str = "core.hydra.io";
pub const CONFIG_VERSION: &str = "v1alpha1";
pub const COMPONENT_CRD: &str = "componentschematics";

fn main() {
...
}

and in another file src/abc.rs, I want use this const.

It doesn't work, whether use :: or not.

println!("{}", COMPONENT_CRD); 
let component_resource = RawApi::customResource(COMPONENT_CRD)
    .within(top_ns.as_str())
    .group(::CONFIG_GROUP)
    .version(::CONFIG_VERSION);

It reports :

    |
208 |         println!("{}", COMPONENT_CRD);
    |                        ^^^^^^^^^^^^^ not found in this scope
error[E0425]: cannot find value `CONFIG_CRD` in this scope
   --> src/abc.rs:209:54
    |
209 |         let config_resource = RawApi::customResource(CONFIG_CRD)
    |                                                      ^^^^^^^^^^ not found in this scope

error[E0425]: cannot find value `CONFIG_VERSION` in the crate root
   --> src/abc.rs:210:24
    |
210 |             .version(::CONFIG_VERSION)
    |                        ^^^^^^^^^^^^^^ not found in the crate root

error[E0425]: cannot find value `CONFIG_GROUP` in the crate root
   --> src/abc.rs:211:22
    |
211 |             .group(::CONFIG_GROUP)
    |                      ^^^^^^^^^^^^ not found in the crate root

Upvotes: 3

Views: 2716

Answers (1)

zrzka
zrzka

Reputation: 21259

I assume that we're talking about Rust 2018 edition. I'd recommend to read the Path clarity section, especially this part:

The prefix :: previously referred to either the crate root or an external crate; it now unambiguously refers to an external crate. For instance, ::foo::bar always refers to the name bar inside the external crate foo.

Use can't use ::CONFIG_VERSION, ::main::CONFIG_VERSION, etc. Couple of options:

  • Use crate::CONFIG_VERSION directly
  • Import it use crate::CONFIG_VERSION and use just CONFIG_VERSION

abc.rs content:

pub(crate) fn foo() {
    println!("{}", crate::CONFIG_VERSION);
}

Another abc.rs variant:

use crate::CONFIG_VERSION;

pub(crate) fn foo() {
    println!("{}", CONFIG_VERSION);
}

main.rs content:

pub(crate) const CONFIG_VERSION: &str = "v1alpha1";

mod abc;

fn main() {
    abc::foo()
}

Upvotes: 2

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