Surprise with array idup method

[Jonathan M Davis]

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