Re: immutable

[Ellery Newcomer]

On 01/26/2011 02:40 PM, Steven Schveighoffer wrote:
On Wed, 26 Jan 2011 15:32:58 -0500, Robert <robert.we...@hotmail.com>
wrote:

Hello,
I have just recently started programming in D (a very pleasant
experience so
far I must say), but when experimenting with the the immutable
attribute I
discovered that the following code does not generate a compile time nor a
runtime error:

//Decalare immutable string
immutable char[] buf = "hello";

//Print the value of buf
writefln("buf = %s",buf);

//Change buf by using standard input
stdin.readln(buf);

//Print buf again
writefln("buf = %s",buf);


This is a bit confusing to be because I had assumed that immutable
data really
would be immutable (without casting). Why does the code above work?


It shouldn't. I don't know where the bug is. Please file a bug with a
complete program (with a main() function) here:
http://d.puremagic.com/issues/enter_bug.cgi

BTW, this has a segfault in Linux, so it's definitely trying to
overwrite immutable data.

-Steve

I'd guess this is the problem:

void badurk(C,E)(ref C[] x, E y){
    x ~= y;
}

void main(string[] args){
    immutable char[] buf = "hello";
    static assert(is(typeof(buf) == immutable(char[])));
    badurk(buf,'a'); //compiler: la la, this is okay!
}



OT: this function confuses me:

size_t readln(C)(ref C[] buf, dchar terminator = '\n') if (isSomeChar!C)
    {
        static if (is(C == char))
        {
            enforce(p && p.handle, "Attempt to read from an unopened 
file.");
            return readlnImpl(p.handle, buf, terminator);
        }
        else
        {
            // TODO: optimize this
            string s = readln(terminator);
            if (!s.length) return 0;
            buf.length = 0;
            foreach (wchar c; s)                      //// <----- (?!)
            {
                buf ~= c;
            }
            return buf.length;
        }
    }