refactor: call_contract_syscall example (#423)

* Added extensive example for call_contract_syscall

* Updated example contract for contract_sys_call

* Updated the info

* Updated the info and contract

* Updated example and information

---------

Co-authored-by: “AkashBalasubramani-Router <“akashb@routerprotocol.com>

Author: Akashneelesh

listings/ch99-starknet-smart-contracts/listing_99_09_call_contract_syscall/src/lib.cairo

@@ -1,31 +1,43 @@
+use starknet::ContractAddress;
 #[starknet::interface]
 trait ITokenWrapper<TContractState> {
     fn transfer_token(
         ref self: TContractState,
-        address: starknet::ContractAddress,
-        selector: felt252,
-        calldata: Array<felt252>
+        address: ContractAddress,
+        sender: ContractAddress,
+        recipient: ContractAddress,
+        amount: u256
     ) -> bool;
 }
 
 #[starknet::contract]
 mod TokenWrapper {
     use super::ITokenWrapper;
+    use serde::Serde;
     use starknet::SyscallResultTrait;
+    use starknet::ContractAddress;
 
     #[storage]
     struct Storage {}
 
     impl TokenWrapper of ITokenWrapper<ContractState> {
         fn transfer_token(
             ref self: ContractState,
-            address: starknet::ContractAddress,
-            selector: felt252,
-            calldata: Array<felt252>
+            address: ContractAddress,
+            sender: ContractAddress,
+            recipient: ContractAddress,
+            amount: u256
         ) -> bool {
-            let mut res = starknet::call_contract_syscall(address, selector, calldata.span())
+            let mut call_data: Array<felt252> = ArrayTrait::new();
+            Serde::serialize(@sender, ref call_data);
+            Serde::serialize(@recipient, ref call_data);
+            Serde::serialize(@amount, ref call_data);
+            let mut res = starknet::call_contract_syscall(
+                address, selector!("transferFrom"), call_data.span()
+            )
                 .unwrap_syscall();
             Serde::<bool>::deserialize(ref res).unwrap()
         }
     }
 }
+

src/ch99-02-02-contract-dispatcher-library-dispatcher-and-system-calls.md

@@ -84,4 +84,6 @@ Using these syscalls can be handy for customized error handling or to get more c
 
 <span class="caption">Listing 99-9: A sample contract using syscalls</span>
 
-To use this syscall, we passed in the contract address, the function selector (which is the `starknet_keccak` hash of the function name), and the calldata (function arguments). At the end, we get returned a serialized value which we'll need to deserialize ourselves!
+To use this syscall, we passed in the contract address, the selector of the function we want to call, and the call arguments.
+
+The call arguments must be provided as an array of `felt252`. To build this array, we serialize the expected function parameters into an `Array<felt252>` using the `Serde` trait, and then pass this array as calldata. At the end, we are returned a serialized value which we'll need to deserialize ourselves!