example: Create an example Config out of the MetadataConfig

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

subxt/examples/metadata_config.rs

@@ -0,0 +1,63 @@
+#![allow(missing_docs)]
+use subxt::{OnlineClient, SubstrateConfig};
+use subxt_core::config::{Config, DefaultExtrinsicParams};
+use subxt_signer::sr25519::dev;
+
+// Generate an interface that we can use from the node's metadata.
+#[subxt::subxt(runtime_metadata_insecure_url = "ws://localhost:9999")]
+pub mod polkadot {}
+
+// Derives aren't strictly needed, they just make developer life easier.
+#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub enum MetadataConfig {}
+
+impl Config for MetadataConfig {
+    // Extracted from metadata directly:
+    type Hash = polkadot::custom_types::Hash;
+    type AccountId = polkadot::custom_types::AccountId;
+    type AssetId = polkadot::custom_types::AssetId;
+    type Address = polkadot::custom_types::Address;
+
+    // Present in metadata but this PoC needs to add
+    // fn specific per name of type to impl the hashing fn.
+    type Hasher = <SubstrateConfig as Config>::Hasher;
+    // Present in metadata but this PoC needs to impl the header
+    // trait to make use of this.
+    type Header = <SubstrateConfig as Config>::Header;
+    // Same story, present in md but needs subxt::tx::Signer<T>.
+    // type Signature = polkadot::custom_types::Signature;
+    type Signature = <SubstrateConfig as Config>::Signature;
+
+    // Not exposed in metadata, seems like heavily involved with
+    // code functionality which cannot safely be expressed in the
+    // metadata.
+    type ExtrinsicParams = DefaultExtrinsicParams<Self>;
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Create a new API client, configured to talk to nodes.
+    let api = OnlineClient::<MetadataConfig>::from_insecure_url("ws://localhost:9999").await?;
+
+    // Build a balance transfer extrinsic.
+    let dest = dev::bob().public_key().into();
+    let balance_transfer_tx = polkadot::tx().balances().transfer_allow_death(dest, 10_000);
+
+    // Submit the balance transfer extrinsic from Alice, and wait for it to be successful
+    // and in a finalized block. We get back the extrinsic events if all is well.
+    let from = dev::alice();
+    let events = api
+        .tx()
+        .sign_and_submit_then_watch_default(&balance_transfer_tx, &from)
+        .await?
+        .wait_for_finalized_success()
+        .await?;
+
+    // Find a Transfer event and print it.
+    let transfer_event = events.find_first::<polkadot::balances::events::Transfer>()?;
+    if let Some(event) = transfer_event {
+        println!("Balance transfer success: {event:?}");
+    }
+
+    Ok(())
+}