I propose that function argument types could be omitted in the same way as
variable and property argument types are omitted when they are set at point of
definition.
At present the type of properties and variables can be inferred as below:
class EvolutionManager {
let proposalManager = ProposalManager() // type is inferred
func proposeTopic(topic: String) {
let evolution = Evolution(topic: topic) // type is inferred
proposalManager.proposeEvolution(evolution)
}
}
However, function arguments cannot be inferred, as below:
class EvolutionManager {
func proposeEvolution(evolution: Evolution, proposalManager =
ProposalManager()) { // compiler error, cannot infer type
proposalManager.proposeEvolution(evolution)
}
}
It's a nice feature of the language that the type can be inferred for
properties and variables, so I don't see any reason not to allow the same for
function arguments. It allows for more concise code, and adds consistency with
other language features. And I don't personally think it would make our code
any harder to read.
There are of course some cases where the type cannot be inferred, i.e. when the
type should actually be a protocol type and the default value is a concrete
type. Consider the following:
protocol ProposalHandler {
associatedType P : Proposable
propose(p: P)
}
class EvolutionManager {
// the type would be inferred as the concrete type `ProposalManager` and
could not be
// called with any other argument type that conforms to the `ProposalHandler`
protocol,
// as may have been the intention
func proposeEvolution(evolution: Evolution, proposalHandler =
ProposalManager())
// instead it should be written as follows:
func proposeEvolution(evolution: Evolution, proposalHandler: ProposalHandler
= ProposalManager())
}
But this is the same for properties and variables, so it should not be a reason
to not allow inferring of function arguments. For example:
class EvolutionManager {
// the property is inferred as the concrete type `ProposalManager` and may not
// be set to any other value of type that conforms to the `ProposalHandler`
protocol,
// as may have been the intention.
var proposalHandler = ProposalManager()
// instead it should be written as follows:
var proposalHandler: ProposalHandler = ProposalManager()
}
What do people think of this?
It would have no impact on existing code, and it's not the kind of thing that
needs an alternative solution.
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