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August 23, 2012
Surprise with array idup method
auto x = [1,2,3];
auto y = x.idup;
y ~= 99;   // fine!
y[0] = 99; // "Error: y[0] isn't mutable"
y.clear;   // fine!


So idup is returning an "immutable(int)[]" rather than an 
"immutable int[]".

I find this a bit surprising. Anybody else?
August 23, 2012
Re: Surprise with array idup method
On Thursday, August 23, 2012 23:55:10 Philip Daniels wrote:
> auto x = [1,2,3];
> auto y = x.idup;
> y ~= 99; // fine!
> y[0] = 99; // "Error: y[0] isn't mutable"
> y.clear; // fine!
> 
> 
> So idup is returning an "immutable(int)[]" rather than an
> "immutable int[]".
> 
> I find this a bit surprising. Anybody else?

It's the same thing that slicing does. The result is tail-const. And since you 
can assign it to immutable int[] if you want to, it's more flexible this way. 
It just means that auto gives you a mutable array with immutable elements 
rather than an immutable array. And if you don't want to care what the type is 
but still want it to be full immutable, then just use immutable rather than 
auto:

immutable y = x.idup;

- Jonathan M Davis
August 23, 2012
Re: Surprise with array idup method
On Thursday, 23 August 2012 at 22:03:04 UTC, Jonathan M Davis 
wrote:
> On Thursday, August 23, 2012 23:55:10 Philip Daniels wrote:
>> auto x = [1,2,3];
>> auto y = x.idup;
>> y ~= 99; // fine!
>> y[0] = 99; // "Error: y[0] isn't mutable"
>> y.clear; // fine!
>> 
>> 
>> So idup is returning an "immutable(int)[]" rather than an
>> "immutable int[]".
>> 
>> I find this a bit surprising. Anybody else?
>
> It's the same thing that slicing does. The result is 
> tail-const. And since you
> can assign it to immutable int[] if you want to, it's more 
> flexible this way.
> It just means that auto gives you a mutable array with 
> immutable elements
> rather than an immutable array. And if you don't want to care 
> what the type is
> but still want it to be full immutable, then just use immutable 
> rather than
> auto:
>
> immutable y = x.idup;
>
> - Jonathan M Davis

Thanks for the explanation Jonathan. Another thing to add to me 
cheat sheet of D-isms :-)
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