如何导入substrate_primitives 以使用sr25519？

Question

I have the following dependencies in my Cargo.toml file:

[package]
name = "api-client-tutorial"
version = "0.1.0"
authors = ["Supercomputing Systems AG <info@scs.ch>"]
edition = "2018"

[dependencies]
substrate-api-client = { git = "https://github.com/scs/substrate-api-client.git" }
codec = { package = "parity-scale-codec", features = ["derive"], version = "1.0.0", default-features = false }

[dependencies.primitives]
git = "https://github.com/paritytech/substrate"
rev = "3bf9540e72df5ecb3955845764dfee7dcdbb26b5"
package = "substrate-primitives"

[dependencies.keyring]
git = "https://github.com/paritytech/substrate"
rev = "3bf9540e72df5ecb3955845764dfee7dcdbb26b5"
package = "substrate-keyring"

I am unsure of the difference between dependencies section and dependencies.primitives section, but the package substrate-primitives is included in the primitives section.

I have seen that substrate_primitives has the module sr25519 I need to use, but when I try to import it in my code:

use substrate_api_client::{Api, node_metadata};
use substrate_primitives::sr25519;
fn main() {
    // instantiate an Api that connects to the given address
    let url = "127.0.0.1:9944";
    // if no signer is set in the whole program, we need to give to Api a specific type instead of an associated type
    // as during compilation the type needs to be defined.
    let api = Api::<sr25519::Pair>::new(format!("ws://{}", url));

    let meta = api.get_metadata();
    println!("Metadata:\n {}", node_metadata::pretty_format(&meta).unwrap());
}

I get the following error:

unresolved import `substrate_primitives`

use of undeclared type or module `substrate_primitives`rustc(E0432)
main.rs(2, 5): use of undeclared type or module `substrate_primitives`

How do I import sr25519 so that I can use the following line in my code?

let api = Api::<sr25519::Pair>::new(format!("ws://{}", url));

Answer 1

The difference between tables under [dependencies] and the [dependencies.primitives] table is that the table for the primitives dependency is not inlined. You could also just inline the primitives dependency and put it under [dependencies] like that:

primitives = { git = "https://github.com/paritytech/substrate", rev = "3bf9540e72df5ecb3955845764dfee7dcdbb26b5", package = "substrate-primitives" }

The toml documentation can give you more details on tables and inline tables.

Regarding your problem. You cannot import the crate like that, because it is renamed to primitives . The package field specifies the real name of the dependency and the table name defines the new name which is used to import it inside your project. For details have a look at the cargo documentation .

Your import should therefore look like this: use primitives::sr25519;