• Domingo (7/7) Oct 30 2014 I spent two days to find a nasty aleatory problem due to a string
• Jesse Phillips (10/17) Oct 30 2014 To recap, the issue is that a char[] buffer is being overridden
• H. S. Teoh via Digitalmars-d-learn (18/26) Oct 30 2014 [...]

"Domingo" <mingodad gmail.com> writes:

I spent two days to find a nasty aleatory problem due to a string 
been assigned a range from a char[] array.

This issue on vibe.d detail it a bit more: 
https://github.com/rejectedsoftware/vibe.d/issues/889

I'm putting it here to call attention for other developers for 
this problem.

Cheers !

"Jesse Phillips" <Jesse.K.Phillips+D gmail.com> writes:

On Friday, 31 October 2014 at 02:04:00 UTC, Domingo wrote:
 I spent two days to find a nasty aleatory problem due to a 
 string been assigned a range from a char[] array.

 This issue on vibe.d detail it a bit more: 
 https://github.com/rejectedsoftware/vibe.d/issues/889

 I'm putting it here to call attention for other developers for 
 this problem.

 Cheers !

To recap, the issue is that a char[] buffer is being overridden 
while a immutable reference was created to the same data (string).

Essentially you can't cast a char[] to string unless it is the 
only reference that will remain. Even so, I wouldn't recommend 
cast in those cases and instead use std.exception.assumeUnique to 
better state the assumption made.



If the mutable reference will remain the duplicating the char[] 
is necessary and the reason for .idup.

"H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:

On Fri, Oct 31, 2014 at 02:03:58AM +0000, Domingo via Digitalmars-d-learn wrote:
 I spent two days to find a nasty aleatory problem due to a string been
 assigned a range from a char[] array.
 
 This issue on vibe.d detail it a bit more:
 https://github.com/rejectedsoftware/vibe.d/issues/889
 
 I'm putting it here to call attention for other developers for this
 problem.

[...]

The problem is not caused by slicing, it's caused by casting a slice of
char[] to string.  Casting char[] to string is a dangerous operation,
because you're operating outside the type system. string is
immutable(char)[], but the original buffer is char[]. Casting it to
string means you're claiming that nobody will modify the char[]
afterwards... but if somebody does modify it later, then you have
violated immutability and broken the type system.

Generally, I recommend using to!string(...) instead of a cast, since
to!string will make a copy of the data if it's not already immutable.
Casts always require extra care because the type system can no longer
help you catch mistakes.


T

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