Possible to defer initialization of let variable?
I thought I saw some Swift code that did this:
let someString : String?
if some things
{
// some stuff
someString = a string from something
// some other stuff
}
// use someString
But I can't get Swift 2 to let me.
Basically, I want to make someString available outside the scope in which it's
initialized, but I don't want its assignment to ever change after that. I could
do the former with var instead of let, of course, but I'd like it to be treated
as a let after the first assignment. Is that possible?
--
Rick Mann
rm...@latencyzero.com
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:08 , Rick Mann rm...@latencyzero.com wrote:
But I can't get Swift 2 to let me.
You’ve left a path through the code that doesn’t set ‘someString’. So, you’ll
need to add:
else
{
someString = nil
}
to the ‘if’.
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:16 , Quincey Morris
quinceymor...@rivergatesoftware.com wrote:
On Jul 7, 2015, at 01:08 , Rick Mann rm...@latencyzero.com wrote:
But I can't get Swift 2 to let me.
You’ve left a path through the code that doesn’t set ‘someString’. So, you’ll
need to add:
else
{
someString = nil
}
to the ‘if’.
Well, I wanted to do this:
// Get the hero thumbnail…
let thumbURL: String?
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
thumbURL = t
break
}
}
print(Thumb: \(thumbURL))
But it complains that it's used before being initialized. I guess I want it to
initialize it to nil, then let me assign it once, then keep it constant.
--
Rick Mann
rm...@latencyzero.com
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:37 , Quincey Morris
quinceymor...@rivergatesoftware.com wrote:
On Jul 7, 2015, at 01:33 , Rick Mann rm...@latencyzero.com wrote:
Yeah, there doesn't seem to be an elegant way to do it
Actually, there is:
let thumbURL: String? =
{
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
return t
}
}
return nil
} ()
Or, if you prefer, instead of using a closure, you can define a nested
function and call it to get the initial value.
I tried it as a closure. The problem arises when you want to initialize more
than one variable in that block of work.
--
Rick Mann
rm...@latencyzero.com
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:49 , Quincey Morris quinceymor...@rivergatesoftware.com wrote: On Jul 7, 2015, at 01:39 , Rick Mann rm...@latencyzero.com wrote: The problem arises when you want to initialize more than one variable in that block of work. If you ask the wrong question, you get a wrong answer. :) Whether or not it was the wrong question is debatable. You can use a tuple: Unfortunately, that requires you to have the values all ready at once. Thanks for trying, but I think there's no good way to do this. Best is to just deal with var. Or do the hacky thing you suggested earlier, with local vars that get assigned at the very end to their lets. -- Rick Mann rm...@latencyzero.com ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:39 , Rick Mann rm...@latencyzero.com wrote:
The problem arises when you want to initialize more than one variable in that
block of work.
If you ask the wrong question, you get a wrong answer. :)
You can use a tuple:
let (thumbURL, isHero) =
{
() - (String?, Bool) in
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
return (t, isHero)
}
}
return (nil, false)
} ()
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Re: Possible to defer initialization of let variable?
Yeah, there doesn't seem to be an elegant way to do it, so I gave up and used a
var.
On Jul 7, 2015, at 01:31 , Quincey Morris
quinceymor...@rivergatesoftware.com wrote:
On Jul 7, 2015, at 01:21 , Rick Mann rm...@latencyzero.com wrote:
let thumbURL: String?
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
thumbURL = t
break
}
}
You’ve still got a path where ‘thumbURL’ is uninitialized — when ‘images’ is
empty. I’m not sure if there’s an elegant way to do it, but you can do it by
brute force something like this:
do
{
var url: String? = nil
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
url = t
break
}
}
thumbURL = url
}
--
Rick Mann
rm...@latencyzero.com
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:33 , Rick Mann rm...@latencyzero.com wrote:
Yeah, there doesn't seem to be an elegant way to do it
Actually, there is:
let thumbURL: String? =
{
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
return t
}
}
return nil
} ()
Or, if you prefer, instead of using a closure, you can define a nested function
and call it to get the initial value.
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Re: Possible to defer initialization of let variable?
On Jul 7, 2015, at 01:21 , Rick Mann rm...@latencyzero.com wrote:
let thumbURL: String?
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
thumbURL = t
break
}
}
You’ve still got a path where ‘thumbURL’ is uninitialized — when ‘images’ is
empty. I’m not sure if there’s an elegant way to do it, but you can do it by
brute force something like this:
do
{
var url: String? = nil
for imgD in images
{
if let isHero = imgD[is_hero] as? Bool where isHero,
let t = imgD[thumbnail_signed_src] as? String
{
url = t
break
}
}
thumbURL = url
}
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Re: Possible to defer initialization of let variable?
If you ask the wrong question, you get a wrong answer. :) Whether or not it was the wrong question is debatable. Honestly I find that assertion suspect considering that you've moved the goalposts three times. ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
