Re: What is the state of scope function parameter?
On Wednesday, 29 March 2017 at 05:15:33 UTC, Ali Çehreli wrote: scope: references in the parameter cannot be escaped (e.g. assigned to a global variable). Ignored for parameters with no references However, it doesn't behave that way. For example, my example here currently is a lie because there is no compilation error with 2.073.2: If you break the rules, even if the compiler doesn't actually catch it, you are still writing illegal code and subject to runtime undefined behavior and/or compilation errors in future versions. The compiler DOES use the scope attribute to optimize out heap allocations in some cases now, which means if you use in improperly you are liable for memory corruption. So maybe it should say "must not" instead of "cannot" since you CAN, it is just broken if you do.
Re: What is the state of scope function parameter?
On Wednesday, 29 March 2017 at 05:15:33 UTC, Ali Çehreli wrote: [..] How would you change the text there? scope: references in the parameter cannot be escaped (e.g. assigned to a global variable) in @safe code when compiled with -dip1000. Ignored for parameters with no references.
Re: What is the state of scope function parameter?
On Wednesday, 29 March 2017 at 05:15:33 UTC, Ali Çehreli wrote:
(More correctly, "scope storage class".)
https://dlang.org/spec/function.html#Parameter
still says
scope: references in the parameter cannot be escaped
(e.g. assigned to a global variable). Ignored for
parameters with no references
However, it doesn't behave that way. For example, my example
here currently is a lie because there is no compilation error
with 2.073.2:
http://ddili.org/ders/d.en/function_parameters.html#ix_function_parameters.scope
What's the truth? How would you change the text there?
Thank you,
Ali
The truth is that almost non of the scope checks are on, unless
you compile with -dip1000:
$ source ~/dlang/dmd-2.073.2/activate
$ dmd ddili_scope_test1.d
$ echo $?
0
$ dmd -dip1000 ddili_scope_test1.d
ddili_scope_test1.d(5): Error: scope variable parameter may not
be returned
Now that's one error, out of two expected, so what's going on
here? As DIP1000 mentions
(https://github.com/dlang/DIPs/blob/master/DIPs/DIP1000.md#safe):
Errors for scope violations are only reported in @safe code.
So if when I changed the code to:
int[] globalSlice;
int[] foo(scope int[] parameter) @safe {
globalSlice = parameter;// ← compilation ERROR
return parameter; // ← compilation ERROR
}
void main() {
int[] slice = [ 10, 20 ];
int[] result = foo(slice);
}
I got:
$ dmd -dip1000 ddili_scope_test1.d
ddili_scope_test1.d(4): Error: scope variable parameter assigned
to non-scope globalSlice
ddili_scope_test1.d(5): Error: scope variable parameter may not
be returned
Just as expected.
Re: What is the state of scope function parameter?
On Tuesday, March 28, 2017 22:15:33 Ali Çehreli via Digitalmars-d-learn wrote: > (More correctly, "scope storage class".) > >https://dlang.org/spec/function.html#Parameter > > still says > >scope: references in the parameter cannot be escaped > (e.g. assigned to a global variable). Ignored for > parameters with no references > > However, it doesn't behave that way. For example, my example here > currently is a lie because there is no compilation error with 2.073.2: > > > http://ddili.org/ders/d.en/function_parameters.html#ix_function_parameters > .scope > > What's the truth? How would you change the text there? > > Thank you, > Ali Not sure when that was changed, since that's not what the spec used to say on scope. IIRC, it used to be that it did not say anything about references and was _very_ vague. But unless something major has changed, _all_ scoped does at this point is make it so that a delegate will not allocate a closure. I'm not sure that it's even properly checked for escaping (though it may be). But scoped has zero effect on other types. Now, I believe that Walter has been working on stuff that would change that, but I don't think that any of that has made it in yet except maybe with a compiler switch intended to separate out the changes until they're ready. - Jonathan M Davis
What is the state of scope function parameter?
(More correctly, "scope storage class".) https://dlang.org/spec/function.html#Parameter still says scope: references in the parameter cannot be escaped (e.g. assigned to a global variable). Ignored for parameters with no references However, it doesn't behave that way. For example, my example here currently is a lie because there is no compilation error with 2.073.2: http://ddili.org/ders/d.en/function_parameters.html#ix_function_parameters.scope What's the truth? How would you change the text there? Thank you, Ali
