On 10/17/2016 11:48 PM, vino wrote:
On Monday, 17 October 2016 at 18:20:00 UTC, cym13 wrote:
On Monday, 17 October 2016 at 18:10:01 UTC, vino wrote:
Hi All,

 As per the book named in the subject it states as below,so can some
one guide me what is wrong in the below code nor correct if my
understanding is wrong.

Page 154
immutable(int[]) specifies that neither the slice nor its elements
can be modified.

So which means that a element or a slice of any array can be
modified, but the below example code is not working.

import std.stdio;
void main() {
immutable(int[]) immSlice = [ 1, 2 ];
immSlice ~= 3;
immSlice[0] = 3; // Error's out at this point
immSlice.length = 1;
writeln(immSlice);
}
From,
Vino.B

I don't see what you don't understand, you said it yourself: "neither
the slice nor its elements can be modified". So you can't modify the
elements  of an immutable array. immSlice is an immutable array of
which you are trying to modify an element.

Hi,

 Thank you for your reply, can you address why the below code is not
working

import std.stdio;

void main() {
int[] Array = [ 1, 2, 3, 4 ];
immutable(int[]) immSlice = Array[ 0 .. 2 ];
writeln("1st : ", immSlice);
immSlice ~= 3;
writeln("2nd : ", immSlice);
immSlice[0] = 3;
writeln("3rd : ", immSlice);
immSlice.length = 1;
writeln("4th : ",immSlice);
}


What is meant in that section in the book is

1) We cannot modify elements of an immutable slice

2) We cannot modify an immutable slice (e.g. cannot add elements to it)

That's the reason for the following three compilation errors:

  Error: cannot modify immutable expression immSlice
  Error: cannot modify immutable expression immSlice[0]
  Error: cannot modify immutable expression immSlice

Your new code has another compilation error here:

    int[] Array = [ 1, 2, 3, 4 ];
    immutable(int[]) immSlice = Array[ 0 .. 2 ];   // <-- ERROR

Error: cannot implicitly convert expression (Array[0..2]) of type int[] to immutable(int[])

That's because immSlice wants to guarantee that it has immutable elements. For that to be true, it cannot share elements of a mutable slice. Otherwise, elements could be modified through Array, which would also change immSlice's elements. (Remember that Array and immSlice would be sharing elements.)

Ali

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