Inputs and Outputs

Inputs

The transpiled Cairo contracts have a different ABI than their Solidity counterparts. Warp allows the use of either the Cairo ABI or the Solidity ABI for passing constructor arguments or function parameters. By default, the Solidity ABI is used.

Using Solidity ABI

The Solidity ABI lets you pass in arguments in a schema similar to what users would use on L1. This is supported in Warp's deploy, invoke and call commands. Warp takes these inputs and transcodes them into Cairo to forward them onto the desired network.

warp invoke <Cairo Contract> --inputs \"ExampleString\",\[1,2,3,4\],-1,100.

Using Cairo ABI

To use the Cairo ABI to pass inputs, add the --use_cairo_abi flag to the deploy, invoke or call command.

Note that there are some nuances that come with using the Cairo ABI:

• Starknet does not support Solidity-style strings, so Warp represents strings as dynamic arrays of bytes. In Cairo ABI, each dynamic array is represented in two parts, the length of the string, and the values of the array <arr_len>,<arr[0],arr[1]...arr[n-1]>. e.g ExampleString -> 13,0x45,0x78,0x61,0x6d,0x70,0x6c,0x65,0x53,0x74,0x72,0x69,0x6e,0x67
• Negative numbers will need to be transformed into their twos complement. e.g to pass -1 into a function that takes int8, -1 needs to be converted to 255 and then passed.
• Data types that are more than 248 bits wide (int256/uint256/bytes32) will need to be split into their lower and upper 128 bits e.g 0x10000000000000000000000000000000f as a uint256 -> 15,1.

warp invoke <Cairo Contract> --use_cairo_abi --inputs 13,0x45,0x78,0x61,0x6d,0x70,0x6c,0x65,0x53,0x74,0x72,0x69,0x6e,0x67,4,1,2,3,4,255,100.

Passing values of different types in both ABIs

The following table represents the ABI for each type in both Solidity and Cairo.

Type	Solidity ABI	Cairo ABI
Signed ints (positive)	7,56	7,56
Signed ints (negative <8bits, 16bits>)	-1,-8	255,65528
Unsigned ints	8,7,56	8,7,56
Strings	\"test\"	4,0x74,0x65,0x73,0x74
Boolean	0,1	0,1
Address	0x000...	0x000...
uint256 (above 128 bits)	0x10000000000000000000000000000000f	15,1
uint256 (below 128 bits)	10	10,0
int256	-257	0xfffffffffffffffffffffffffffffeff,0xffffffffffffffffffffffffffffffff
Fixed Size Array (ex: uint8[6])	[0,1,2,3,4,5]	0,1,2,3,4,5
Dynamic Array (ex: uint8[])	[1,2,3,4]	4,1,2,3,4
Struct (ex: {uint, uint})	[1,2]	1,2

Note: In both Solidity and Cairo ABI, numbers can also be passed as hex values

Outputs

The outputs will always be in Cairo ABI.

The following Solidity contract named example.sol will be used to illustrate the feature:

pragma solidity ^0.8;

contract foo {
  uint256 public x;

  string public y;

  constructor(uint256 _x, string memory _y) {
    x = _x;
    y = _y;
  }
}

Transpile the contract:

warp transpile example.sol

Deploy the contract:

warp deploy warp_output/example__WC__foo.cairo --inputs 5,\"test\"

call the contract to get the outputs:

$: warp call warp_output/example__WC__foo.cairo --function x --address 0x01563072fb9a5ce43c5610d205dd815051714d9949104db009a0bbd3ff71c75f
5 0

$: warp call warp_output/example__WC__foo.cairo --function y --address 0x01563072fb9a5ce43c5610d205dd815051714d9949104db009a0bbd3ff71c75f
4 116 101 115 116

Dynamic Array as Inputs and Outputs

Dynamic arrays are fully supported as inputs and outputs to transpiled contracts. The only limitation of using this data type as an input or output is that dynamic arrays cannot be used in another reference type. e.g A struct where a member is a dynamic array or an array of dynamic arrays.