[fix] hyperledger-iroha#1917: Add easy_from_str_impl macro (hyperledg…

…er-iroha#2054)

Signed-off-by: Sam H. Smith <[email protected]>

CONTRIBUTING.md

@@ -12,8 +12,8 @@ The following is a short set of guidelines for contributing to Iroha.
 * Fork [Iroha](https://github.com/hyperledger/iroha/tree/iroha2-dev).
 * Fix your issue of choice.
 * Write [tests](https://doc.rust-lang.org/cargo/commands/cargo-test.html). Ensure they all pass (`cargo test`).
-* Fix [`clippy`](https://lib.rs/crates/cargo-lints) warnings: `cargo lints clippy --workspace --tests --benches`
-* Format code `cargo fmt --all` and generate docs `cargo run --bin iroha_docs >"docs/source/references/config.md" && git add "docs/source/references/config.md"`
+* Fix [`clippy`](https://lib.rs/crates/cargo-lints) warnings: `cargo lints clippy --workspace --benches --tests --examples --all-features`
+* Format code `cargo +nightly fmt --all` and generate docs `cargo run --bin iroha_docs >"docs/source/references/config.md" && git add "docs/source/references/config.md"`
 * `git pull -r hyperledger iroha2-dev`, `git commit -s`, `git push <your-fork>`, and [create a pull request](https://github.com/hyperledger/iroha/compare) to the `iroha2-dev` branch on GitHub.
 
 ### Reporting Bugs

data_model/src/asset.rs

@@ -150,21 +150,31 @@ pub enum AssetValueType {
     Store,
 }
 
-impl FromStr for AssetValueType {
-    type Err = &'static str;
-
-    fn from_str(value_type: &str) -> Result<Self, Self::Err> {
-        // TODO: Could be implemented with some macro
-        match value_type {
-            "Quantity" => Ok(AssetValueType::Quantity),
-            "BigQuantity" => Ok(AssetValueType::BigQuantity),
-            "Fixed" => Ok(AssetValueType::Fixed),
-            "Store" => Ok(AssetValueType::Store),
-            _ => Err("Unknown variant"),
+/// A declarative macro that implements `FromStr` for a given
+/// C like enumeration. The macro is invoked like follows:
+/// `easy_from_str_impl! { NameOfEnum, EnumVariation1, EnumVariation2, ... }`
+macro_rules! easy_from_str_impl {
+    (eval_to $cmp:expr, $enum_type:ty, $enum_value:tt) => {
+        if $cmp == stringify!($enum_value) {
+            return Ok(<$enum_type>::$enum_value);
         }
-    }
+    };
+    ($enum_type:ty, $( $enum_value:tt ),+ ) => {
+        impl FromStr for $enum_type {
+            type Err = &'static str;
+
+            fn from_str(value_type: &str) -> Result<Self, Self::Err> {
+                $(
+                    easy_from_str_impl!{eval_to value_type, $enum_type, $enum_value}
+                )+
+                return Err(concat!("Unknown variant for type ", stringify!($enum_type)));
+            }
+        }
+    };
 }
 
+easy_from_str_impl! {AssetValueType, Quantity, BigQuantity, Fixed, Store}
+
 /// Asset's inner value.
 #[derive(
     Debug, Clone, PartialEq, Eq, Decode, Encode, Deserialize, Serialize, FromVariant, IntoSchema,