[swift-users] Protocol with instance var that's set on construction, otherwise read-only

[Rick Mann]

It complains if I make it a let because computed properties must be var. Because it's a protocol, it can't be stored (even though it can be stored in the conforming type).

If I make it { get }, I can't set it in the extensions init() method.

I guess I could make it private set (not sure of the syntax for that), but it still doesn't have let semantics.

> On Aug 2, 2016, at 16:28 , David Sweeris <davesweeris at mac.com> wrote:
> 
> If I understand things correctly, you *can* make uuid a let because you’re allowed to set them (once) during init functions.
> 
> - Dave Sweeris
> 
>> On Aug 2, 2016, at 6:22 PM, Rick Mann via swift-users <swift-users at swift.org> wrote:
>> 
>> I'm trying to define a protocol that has a read-only, immutable member "uuid" that can be set in the init() method, but I'm having trouble. I have this:
>> 
>> protocol
>> Element
>> {
>>   var uuid : { get }
>> }
>> 
>> extension
>> Element
>> {
>>   init(...)
>>   {
>> 	self.uuid = ...
>>   }
>> }
>> 
>> I can't make it let, because they're computed.
>> 
>> I'm realizing from other stuff that I really can't have the init(...) method in the extension, anyway. But I'd really like to be able to specify a let member in the protocol. What's the best way to have that effect?
>> 
>> In my semantics, an Element has a uniquely-assigned uuid. It might be generated when the object is instantiated, or it might be deserialized from disk, but once that's done, it can never change. How do I express that?
>> 
>> Thanks,
>> 
>> -- 
>> Rick Mann
>> rmann at latencyzero.com
>> 
>> 
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>> swift-users at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
> 


-- 
Rick Mann
rmann at latencyzero.com