On Monday, 5 August 2013 at 13:54:38 UTC, Adam D. Ruppe wrote:
On Monday, 5 August 2013 at 13:42:01 UTC, Michal Minich wrote:
But what Bosak proposes is that when "with" statements ends,
the object should be destructed
That would happen if the object is a struct, or wrapped in a
struct, since it would go out of scope at the end of the with
and call its destructor then.
So then you could just go
import std.typecons;
with(auto a = Scoped!T()) { ... }
and the Scoped destructor does the deleting.
Exactly. My idea is to add third use case of with. Not there are
2 ways to use with(of witch I know):
1) Declare something and use with to not repeat yourself:
auto foo = new Foo;
with(foo) {
name = "bar"; //foo.name = "bar";
}
In this case it is only used for object construction and setup.
And the with statement doesn't destruct the object or anything
like that.
2) Used with types
struct Foo {
static int bar = 2;
}
with(Foo) {
bar++; //Foo.bar++;
}
Again with doesn't destruct or anything
All of the above are currently available, but I want a third case
to be added:
3) Used when you declare something in the with statement with
scope only in the with statement
with(Foo foo = new Foo) {
name = "bar";
}
After that foo's destructor gets called and since foo was in the
scope of with it goes out of scope and no references are made to
foo. There should be a constraint that you cannot take the
address of foo in the with statement(i.e assign a global to foo)
3.1) Or used with rvalues??
int[] values;
with(new Foo) {
name = "bar";
values = getData(); //foo.getData()
}
//use values taken from foo
I think that in case 3.1 it is very intuitive for using resources
like files. Instead of writing something like:
string text;
auto file = open("myfile.txt", "r");
text = t.readlines();
file.close();
You can write this:
string text;
with(open("myfile.txt", "r")) { //no need to declare variable
text = readlines(); //just use the file to get the data
}//with automaticaly calls close() on the file, even if exception
got thrown
And if the exception got thrown in the declaration of the with
block, then the with block doesn't execute. For example in the
above code if the file didn't exist, an exception would be thrown
from open and no variable would be created.
I hope that I have made my suggestion more clear.
