Re: Range question
18.02.2012 2:50, H. S. Teoh пишет: ... You cannot have ref local variable, so e is a copy in any case. It may be a class reference or a pointer, so calling potentially non-const methods is probably not safe here, but assignment shouldn't give you problems.
Re: Range question
On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote: 18.02.2012 2:50, H. S. Teoh пишет: ... You cannot have ref local variable, so e is a copy in any case. It may be a class reference or a pointer, so calling potentially non-const methods is probably not safe here, but assignment shouldn't give you problems. But that's the problem, if e is a dynamic array, then it can potentially be modified through the original reference after being assigned. Ideally, I'd need e to be a reference to an immutable type. But that requires a way of converting an arbitrary type to its immutable form, which I don't know how to do in a generic way. T -- Let's eat some disquits while we format the biskettes.
Re: Range question
18.02.2012 7:51, H. S. Teoh пишет:
On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote:
18.02.2012 2:50, H. S. Teoh пишет:
...
You cannot have ref local variable, so e is a copy in any case. It
may be a class reference or a pointer, so calling potentially
non-const methods is probably not safe here, but assignment
shouldn't give you problems.
But that's the problem, if e is a dynamic array, then it can potentially
be modified through the original reference after being assigned.
Ideally, I'd need e to be a reference to an immutable type. But that
requires a way of converting an arbitrary type to its immutable form,
which I don't know how to do in a generic way.
T
I see. But you can't have a generic copy operation either, due to
possibly complicated memory model of your program. You'd need a proper
copy construction for that, but there is no way to check for it's
correctness in generic type. I'd just use constraint to limit a range
underlying type to immutable, something like:
template isImmutable(T) {
static if( is( T == immutable T ) ) {
enum isImmutable = 1;
} else {
enum isImmutable = 0;
}
}
...
if( isImmutable!(ElementType!T) )
...
Re: Range question
On Sat, Feb 18, 2012 at 08:02:15AM +0200, Mantis wrote:
18.02.2012 7:51, H. S. Teoh пишет:
On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote:
18.02.2012 2:50, H. S. Teoh пишет:
...
You cannot have ref local variable, so e is a copy in any case. It
may be a class reference or a pointer, so calling potentially
non-const methods is probably not safe here, but assignment
shouldn't give you problems.
But that's the problem, if e is a dynamic array, then it can
potentially be modified through the original reference after being
assigned.
Ideally, I'd need e to be a reference to an immutable type. But that
requires a way of converting an arbitrary type to its immutable form,
which I don't know how to do in a generic way.
[...]
I see. But you can't have a generic copy operation either, due to
possibly complicated memory model of your program. You'd need a proper
copy construction for that, but there is no way to check for it's
correctness in generic type.
True.
I'd just use constraint to limit a range underlying type to immutable,
something like:
template isImmutable(T) {
static if( is( T == immutable T ) ) {
enum isImmutable = 1;
} else {
enum isImmutable = 0;
}
}
...
if( isImmutable!(ElementType!T) )
...
Hmm. But the problem is that I want to be able to handle something like
File.byLine(). Or perhaps what I really need is just to write a wrapper
around File.readln() that ensures immutability, then I can use
isImmutable() to enforce safety in the algorithm, and just pass the
wrapper when I need to use an underlying File.
T
--
MAS = Mana Ada Sistem?
Re: Range question
On Friday, February 17, 2012 22:27:06 H. S. Teoh wrote:
Hmm. But the problem is that I want to be able to handle something like
File.byLine(). Or perhaps what I really need is just to write a wrapper
around File.readln() that ensures immutability, then I can use
isImmutable() to enforce safety in the algorithm, and just pass the
wrapper when I need to use an underlying File.
If you need to handle arrays differently, then just use a static if to
specialize the appropriate section of code for them. So, something like
ElementType!R choose(R, E)(R range)
if(isInputRange!R)
{
Unqual!(ElementType!R) e;
foreach(e; range)
{
if(/* some criterion */)
{
static if(isDynamicArray!(ElementType!R)
is(Unqual!(ElementType!R) == ElementType!R))
{
e = range.front.dup;
}
else
e = range.front;
}
}
return cast(ElementType!R)e;
}
- Jonathan M Davis
