docs: document struct coded and add examples (#406)

* docs: document struct coded and add examples

* refactor: move struct encoding to new misc section

* fix: dont indent examples

* chore: nits

* Update src/reference/cast/cast-send.md

Co-authored-by: Bjerg <onbjerg@users.noreply.github.com>

* Update src/reference/cast/cast-send.md

Co-authored-by: Bjerg <onbjerg@users.noreply.github.com>

src/SUMMARY.md

@@ -265,3 +265,4 @@
       - [`addr`](./cheatcodes/addr.md)
       - [`sign`](./cheatcodes/sign.md)
       - [`label`](./cheatcodes/label.md)
+- [Misc](./misc/README.md)

src/misc/README.md

@@ -0,0 +1,3 @@
+## Misc
+
+- [Struct encoding](./struct-encoding.md)

src/misc/struct-encoding.md

@@ -0,0 +1,63 @@
+## Struct Encoding
+
+Structs are user defined types that can group several variables:
+
+```solidity
+struct MyStruct {
+    address addr;
+    uint256 amount;
+}
+```
+
+Only the new [ABI coder v2](https://docs.soliditylang.org/en/latest/layout-of-source-files.html#abi-coder-pragma) can encode and decode arbitrarily nested arrays and structs. Since Solidity 0.8.0 it is activated by default, prior to that it needs to be activated via `pragma experimental ABIEncoderV2`.
+
+Solidity structs map to the ABI type "tuple". For more information on how Solidity types map to ABI types see [Mapping Solidity to ABI types](https://docs.soliditylang.org/en/latest/abi-spec.html#mapping-solidity-to-abi-types) in the Solidity documentation.
+
+Structs are therefore encoded and decodes as tuples. So the struct we defined above, `MyStruct`, maps to the tuple `(address,uint256)` in terms of the ABI.
+
+Let's see how this works in a contract:
+
+```solidity
+pragma solidity =0.8.15;
+
+
+contract Test {
+    struct MyStruct {
+        address addr;
+        uint256 amount;
+    }
+    function f(MyStruct memory t) public pure {}
+}
+```
+
+The ABI of the `f` function in this contract is:
+
+```json
+{
+	"inputs": [
+		{
+			"components": [
+				{
+					"internalType": "address",
+					"name": "addr",
+					"type": "address"
+				},
+				{
+					"internalType": "uint256",
+					"name": "amount",
+					"type": "uint256"
+				}
+			],
+			"internalType": "struct Test.MyStruct",
+			"name": "t",
+			"type": "tuple"
+		}
+	],
+	"name": "f",
+	"outputs": [],
+	"stateMutability": "pure",
+	"type": "function"
+}
+```
+
+which reads: The function `f` takes 1 input of type `tuple` with two components of type `address` and `uint256`.

src/reference/cast/cast-send.md

@@ -52,6 +52,23 @@ The destination (*to*) can be an ENS name or an address.
     cast send --ledger 0x... "deposit(address,uint256)" 0x... 1
     ```
 
+3. Call a function that expects a `struct`:
+
+    ```solidity
+    contract Test {
+        struct MyStruct {
+            address addr;
+            uint256 amount;
+        }
+        function myfunction(MyStruct memory t) public pure {}
+    }
+    ```
+
+    Structs are encoded as tuples (see [struct encoding](./reference/common/struct-encoding.md))
+
+    ```sh
+    cast send "myfunction((address,uint256))" 0x... "(0x...,1)"
+    ```
 ### SEE ALSO
 
-[cast](./cast.md), [cast call](./cast-call.md), [cast publish](./cast-publish.md), [cast receipt](./cast-receipt.md)
+[cast](./cast.md), [cast call](./cast-call.md), [cast publish](./cast-publish.md), [cast receipt](./cast-receipt.md), [struct encoding](./misc/struct-encoding.md)

src/reference/cast/cast-sig.md

@@ -25,6 +25,23 @@ The signature (*sig*) is a fragment in the form `<function name>(<types...>)`.
     cast sig "transfer(address,uint256)"
     ```
 
+2. Get the selector for a function that expects a `struct`:
+
+    ```solidity
+    contract Test {
+        struct MyStruct {
+            address addr;
+            uint256 amount;
+        }
+        function myfunction(MyStruct memory t) public pure {}
+    }
+    ```
+
+    Structs are encoded as tuples (see [struct encoding](./reference/common/struct-encoding.md)).
+
+    ```sh
+    cast sig "myfunction((address,uint256))"
+    ```
 ### SEE ALSO
 
-[cast](./cast.md)
+[cast](./cast.md), [struct encoding](./misc/struct-encoding.md)