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digitalmars.D.bugs - [Issue 7161] New: Passing string literal by ref changes its bounds forever

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7161

           Summary: Passing string literal by ref changes its bounds
                    forever
           Product: D
           Version: D1 & D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: verylonglogin.reg gmail.com


--- Comment #0 from Denis <verylonglogin.reg gmail.com> 2011-12-24 15:41:24 MSK
---
---
import std.stdio;

void f(ref string s) {
    writeln(s);
    if(s.length)
        --s.length;
    else
        s = "def";
}

void g1() { f("abc"); }
void g2() { f("abc"); }

void main()
{
    g1();     // prints "abc"
    g2();     // prints "ab"
    f("abc"); // prints "a"
    f("abc"); // prints ""
    f("abc"); // prints "def"
}
---

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next sibling parent d-bugmail puremagic.com writes:
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Denis <verylonglogin.reg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


--- Comment #1 from Denis <verylonglogin.reg gmail.com> 2011-12-24 15:54:03 MSK
---
Workaround:
wrap every passed string `f("abc")` like `f(s("abc"))` and `f("11", "22",
"33")` like `f(s("11"), s!1("22"), s!2("33"))` where `s` is:
---
ref string s(size_t n = 0)(string s) {
    static string ss;
    ss = s;
    return ss;
}
---

It does have an easy workaround but is very annoying.

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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com


--- Comment #2 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2011-12-24
05:21:38 PST ---
I'll do you one better:

void g1() { f("abc".s); }
void g2() { f("abc".s); }

ref string s_impl()(string s)
{
    static string ss;
    ss = s;
    return ss;    
}

ref string s(string s) 
{
    return s_impl!()(s);
}

void main()
{
    g1();     
    g2();     
    f("abc".s);
    f("abc".s);
    f("abc".s);
}

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2011-12-24
05:27:20 PST ---
Actually s_impl isn't needed, s() can have that implementation it just needs a
set of empty parens:
ref string s()(string s) 
{
    static string ss;
    ss = s;
    return ss;    
}

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--- Comment #4 from Denis <verylonglogin.reg gmail.com> 2011-12-24 17:03:56 MSK
---
And a better one (CTFE friendly, no need to specify param number):
---
private ref string wrap(string s) {
    static struct GCString { string str; }
    auto gcStr = new GCString();
    gcStr.str = s;
    return gcStr.str;
}
---
Yes, hello Java-like arrays!

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Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com


--- Comment #5 from Jonathan M Davis <jmdavisProg gmx.com> 2011-12-24 13:11:00
PST ---
This code shouldn't even be legal. A string literal isn't an lvalue and can't
be passed by reference. It's bug that that compiles at all. This looks like a
duplicate of bug# 4539.

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Denis <verylonglogin.reg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


--- Comment #6 from Denis <verylonglogin.reg gmail.com> 2011-12-25 13:49:32 MSK
---
*** This issue has been marked as a duplicate of issue 4539 ***

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