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FuelLabs · Sep 20, 2023 · d5cf8d6 · d5cf8d6
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diff --git a/docs/src/types/custom_types.md b/docs/src/types/custom_types.md
@@ -59,3 +59,44 @@ Your Rust code would look like this:
 ```rust,ignore
 {{#include ../../../packages/fuels/tests/types_contracts.rs:generic}}
 ```
+
+### Unused generic type parameters
+Sway supports unused generic type parameters when declaring structs/enums:
+```Rust
+struct SomeStruct<T, K> {
+  field: u64
+}
+
+enum SomeEnum<T, K> {
+  One: u64
+}
+
+```
+
+If you tried the same in Rust you'd get complaints that `T` and `K` must be used or removed. When generating Rust bindings for such types we make use of the [`PhantomData`](https://doc.rust-lang.org/std/marker/struct.PhantomData.html#unused-type-parameters) type.
+
+The generated bindings for the above example would look something like this:
+```Rust
+struct SomeStruct<T, K> {
+   pub field: u64,
+   pub _unused_generic_0: PhantomData<T>
+   pub _unused_generic_1: PhantomData<K>
+}
+
+enum SomeEnum<T, K> {
+  One(u64),
+  IgnoreMe(PhantomData<T>, PhantomData<K>)
+}
+```
+
+To lessen the impact to DEX you may use `SomeStruct::new` to initialize the above structure without bothering with the `PhantomData`s:
+```rust,ignore
+{{#include ../../../examples/types/src/lib.rs:unused_generics_struct}}
+```
+
+If your struct doesn't have any fields we'll also derive `Default`.
+
+As for enums all `PhantomData`s are placed inside a new variant called `IgnoreMe` which you'll need to ignore in your matches:
+```rust,ignore
+{{#include ../../../examples/types/src/lib.rs:unused_generics_enum}}
+```
diff --git a/examples/types/src/lib.rs b/examples/types/src/lib.rs
@@ -166,4 +166,157 @@ mod tests {
         // ANCHOR_END: type_conversion
         Ok(())
     }
+
+    #[tokio::test]
+    async fn unused_generics() -> Result<()> {
+        use fuels::prelude::*;
+        abigen!(Contract(
+            name = "MyContract",
+            abi = r#" {
+  "types": [
+    {
+      "typeId": 0,
+      "type": "()",
+      "components": [],
+      "typeParameters": null
+    },
+    {
+      "typeId": 1,
+      "type": "enum MyEnum",
+      "components": [
+        {
+          "name": "One",
+          "type": 7,
+          "typeArguments": null
+        }
+      ],
+      "typeParameters": [
+        3,
+        2
+      ]
+    },
+    {
+      "typeId": 2,
+      "type": "generic K",
+      "components": null,
+      "typeParameters": null
+    },
+    {
+      "typeId": 3,
+      "type": "generic T",
+      "components": null,
+      "typeParameters": null
+    },
+    {
+      "typeId": 4,
+      "type": "struct MyStruct",
+      "components": [
+        {
+          "name": "field",
+          "type": 7,
+          "typeArguments": null
+        }
+      ],
+      "typeParameters": [
+        3,
+        2
+      ]
+    },
+    {
+      "typeId": 5,
+      "type": "u16",
+      "components": null,
+      "typeParameters": null
+    },
+    {
+      "typeId": 6,
+      "type": "u32",
+      "components": null,
+      "typeParameters": null
+    },
+    {
+      "typeId": 7,
+      "type": "u64",
+      "components": null,
+      "typeParameters": null
+    },
+    {
+      "typeId": 8,
+      "type": "u8",
+      "components": null,
+      "typeParameters": null
+    }
+  ],
+  "functions": [
+    {
+      "inputs": [
+        {
+          "name": "arg",
+          "type": 4,
+          "typeArguments": [
+            {
+              "name": "",
+              "type": 8,
+              "typeArguments": null
+            },
+            {
+              "name": "",
+              "type": 5,
+              "typeArguments": null
+            }
+          ]
+        },
+        {
+          "name": "arg_2",
+          "type": 1,
+          "typeArguments": [
+            {
+              "name": "",
+              "type": 6,
+              "typeArguments": null
+            },
+            {
+              "name": "",
+              "type": 7,
+              "typeArguments": null
+            }
+          ]
+        }
+      ],
+      "name": "test_function",
+      "output": {
+        "name": "",
+        "type": 0,
+        "typeArguments": null
+      },
+      "attributes": null
+    }
+  ],
+  "loggedTypes": [],
+  "messagesTypes": [],
+  "configurables": []
+}"#
+        ));
+
+        // ANCHOR: unused_generics_struct
+        assert_eq!(
+            <MyStruct<u16, u32>>::new(15),
+            MyStruct {
+                field: 15,
+                _unused_generic_0: std::marker::PhantomData,
+                _unused_generic_1: std::marker::PhantomData
+            }
+        );
+        // ANCHOR_END: unused_generics_struct
+
+        let my_enum = <MyEnum<u32, u64>>::One(15);
+        // ANCHOR: unused_generics_enum
+        match my_enum {
+            MyEnum::One(_value) => {}
+            MyEnum::IgnoreMe(..) => panic!("Will never receive this variant"),
+        }
+        // ANCHOR_END: unused_generics_enum
+
+        Ok(())
+    }
 }
diff --git a/packages/fuels/tests/types_contracts.rs b/packages/fuels/tests/types_contracts.rs
@@ -1399,21 +1399,6 @@ async fn test_identity_with_two_contracts() -> StdResult<(), Box<dyn std::error:
     Ok(())
 }
 
-// #[test]
-// fn feature() {
-//     let code = Abigen::generate(
-//         vec![AbigenTarget {
-//             name: "MyContract".to_string(),
-//             abi: "tests/types/contracts/generics/out/debug/generics-abi.json".into(),
-//             program_type: fuels_code_gen::ProgramType::Contract,
-//         }],
-//         false,
-//     )
-//     .unwrap();
-//
-//     std::fs::write("/home/segfault_magnet/the_code.rs", code.to_string()).unwrap();
-// }
-
 #[tokio::test]
 async fn generics_test() -> Result<()> {
     setup_program_test!(