On 07/06/2012 05:14 AM, lijie wrote:
On Thu, Jul 5, 2012 at 4:26 PM, Denis Shelomovskij
<[email protected] <mailto:[email protected]>> wrote:
Different situation is for such C# loop:
---
for (int i = 0; i < funcs.Length; ++i)
{
int t = i;
funcs[i] = new MyFunc(() => System.Console.WriteLine(t));
}
---
where "t" is local for scope. Here C# behaves correctly, but D
doesn't. This D loop
---
foreach(i; 0 .. 5) {
int t = i;
functions ~= { printf("%d\n", t); };
}
---
prints "4" five times. It's Issue 2043:
http://d.puremagic.com/issues/__show_bug.cgi?id=2043
<http://d.puremagic.com/issues/show_bug.cgi?id=2043>
How to distinguish which variables will be copied to the closure context?
They are not copied, they are stored there.
I think this is a scope rule, in the previous code, there are three
variables:
1. function arguments
2. loop variables
3. local variables
Seems only function parameters is copied. In C#, local variables is
copied. There are other rules? And why is the loop variable not local?
Thanks.
Best regards,
-- Li Jie
It is simple. Variable declarations introduce a new variable. Closures
that reference the same variable will see the same values.
----
foreach(i; 0..3) { functions~={writeln(i);}; }
is the same as
for(int i=0;i<3;i++) { functions~={writeln(i);}; }
is the same as
{int i=0;for(;i<3;i++) { functions~={writeln(i);}; }}
is the same as
{
int i=0;
{ functions~={writeln(i);}; }
i++;
{ functions~={writeln(i);}; }
i++;
{ functions~={writeln(i);}; }
i++;
}
----
foreach(i; 0..3){ int j=i; functions~={writeln(j);}; }
is the same as
for(int i=0;i<3;i++){ int j=i; functions~={writeln(j);}; }
is the same as
{int i=0;for(i<3;i++){ int j=i; functions~={writeln(j);}; }
is the same as
{
int i=0;
{ int j=i; functions~={writeln(j);}; }
i++;
{ int j=i; functions~={writeln(j);}; }
i++;
{ int j=i; functions~={writeln(j);}; }
i++;
}
----
I think it is quite intuitive.
