I believe this should work if you declare an init(arrayLiteral: constructor (or descend the protocol from IExpressibleByArrayLiteral, which declared said .ctor; I;m not sure if that step is necessary or optional).
if this does not work, that’d be a bug, I think.
Note that on Toffee, you currently cannot implement interfaces one structs; this is a runtime limitation and will be solved for Toffee V2; On Java, .NET and Island, that will be fine.