External
External variables are provided to the FCT Engine as an array of bytes32 values by the activator. This values might contain any native type, e.g. uint256, bytes32, address, bool, etc.
Usage
0xFC000....0000LLLL LLLL holds the variable index inside the provided variable array (starting with 1)
External variable use four range of values:
For address types:
0xFC00000000000000000000000000000000000001
...
0xFC0000000000000000000000000000000000ffff
For uint256 and bytes32 types:
0xFC00000000000000000000000000000000000000000000000000000000000001
...
0xFC0000000000000000000000000000000000000000000000000000000000ffff
FC stands for "Future Changeable"
The activator sets values for variables when executing the FCT. Be careful when using external variables.
A common use case is to build p2p swap FCT with two calls. The first one, for example, sending X tokens a variables address (0xFC...0001) and the second one is getting Y ether from that address (0xFC.....0001)
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