On 12.04.2017 7:19, Jaden Geller wrote:
On Apr 7, 2017, at 4:07 AM, Vladimir.S via swift-evolution
<[email protected] <mailto:[email protected]>> wrote:
On 07.04.2017 10:21, Daniel Duan via swift-evolution wrote:
Hi all,
In a discussion about inferring parameter types from default value,
Slava brought up some performance problems caused by type inference for
stored properties in side types:
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170313/033882.html
Towards the end, the post mentioned that some Swift team members
contemplated requiring types for stored properties in type declarations.
I think this idea deserves some more attention. Hence this last minute
idea-floating.
In addition to solving a performance headache in implementation,
there're always the general benefit of making type declartion more
explicit and readable (clarity for reader should out-weigh pleasure of
the author). Making the language slightly more consistent (we are not
inferring types for default parameter values in function anyways).
The cons for doing this are obvious too: the inference makes the
language feels more friendly and is, undoubtedly, a beloved feature for
many. This would be a source breaking change.
Just thought I'd float the idea to gather some quick reaction. What do
y'all think?
Although it seems like only an implementation-side problem(i.e. "let's just improve
implementation"), I see a benefits to require type for stored property *if* it is
not obvious what the type is for *reader*. I.e. if we have something like this, I
don't think we should require a type:
struct S {
var x = 0
}
I think there is value in requiring a type annotation there. For example, this bug
would be avoided: https://twitter.com/benjaminencz/status/851892622213783552
I believe the pointed problem is much wider, than type-inference and I even think
this is bug(in design?) that should be fixed at least with warning.
Please consider this example:
protocol P {
var value : Int32 {get}
}
extension P {
var value : Int32 {return 20}
}
class C : P {
let value = 4_000_000_000
/// or even this:
// let value : Int = 4_000_000_000
}
First, as class C conforms to P protocol, it must have *mutable* 'value'
property
Second, currently it seems like class C has two 'value' properties with different
type. It is very strange(the principle of less surprise, yes?) and as we can see
dangerous behavior. Was bug to bugs.swift.org submitted? If so, what was the reply of
the core team?
but I do think it will be better to require a type in such cases :
struct S{
var x = something(SomeType(), 123, "123") // can be generic func
}
Daniel Duan _______________________________________________
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