Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 19:59:52 UTC, Joseph wrote: The compiler shouldn't arbitrarily force one to make arbitrary decisions that waste time and money. Like having a type system? Having to do *cast(int*)&s to interpret a string as an int isn't strictly necessary, and wastes dev time when they have to type extra letters. Throwing an exception when there are import cycles that may cause problems is absolutely the correct thing to do. It's a choice between hard-to-figure-out errors that may depend on the order in which files were passed to the linker, and getting an exception before you've even started running your tests. If we could get this message at compile-time, that would of course be better, but that cannot be done in the general case due to separate compilation. If you want such a message in the cases where it is possible, feel free to create a pull request. It would be possible to add a way to say 'ignore cycles for this module ctor', but as has been pointed out, cycles are generally a symptom of poor architecture, are brittle, and can almost always be avoided (and when they can't, there's a way around that too). -- Biotronic
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 19:59:52 UTC, Joseph wrote:
On Tuesday, 12 September 2017 at 10:08:11 UTC, Moritz Maxeiner
wrote:
[...]
The compiler shouldn't arbitrarily force one to make arbitrary
decisions that waste time and money.
My solution was to turn those static this's in to functions and
simply call them at at the start of main(). Same effect yet
doesn't crash. The compiler should only run the static this's
once per module load anyways, right? If it is such a problem
then some way around it should be included: @force static
this() { } ? The compiler shouldn't make assumptions about the
code I write and always choose the worse case, it becomes an
unfriendly relationship at that point.
Solution is to redesign so there is no cycle because it is
brittle and generally due to poor architecture. Like goto cyclic
dependencies are occasionally useful, rarely necessary and avoid
by default.
bye,
lobo
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 19:59:52 UTC, Joseph wrote:
The compiler shouldn't arbitrarily force one to make arbitrary
decisions that waste time and money.
You might want to educate yourself about arbitrary decisions that
waste time and money:
https://isocpp.org/wiki/faq/ctors#static-init-order
My solution was to turn those static this's in to functions and
simply call them at at the start of main(). Same effect yet
doesn't crash. The compiler should only run the static this's
once per module load anyways, right? If it is such a problem
then some way around it should be included: @force static
this() { } ?
There is a way, turn static this's into functions and simply call
them at the start of main().
The compiler shouldn't make assumptions about the code I write
and always choose the worse case, it becomes an unfriendly
relationship at that point.
If you want C++, you know where to find it, although I wouldn't
exactly call it "friendly".
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 19:59:52 UTC, Joseph wrote:
On Tuesday, 12 September 2017 at 10:08:11 UTC, Moritz Maxeiner
wrote:
On Tuesday, 12 September 2017 at 09:11:20 UTC, Joseph wrote:
I have two nearly duplicate files I added a static this() to
initialize some static members of an interface.
On one file when I add an empty static this() it crashes
while the other one does not.
The exception that happens is
Cyclic dependency between module A and B.
Why does this occur on an empty static this? Is it being ran
twice or something? Anyway to fix this?
The compiler errors because the spec states [1]
Each module is assumed to depend on any imported modules
being statically constructed first
, which means two modules that import each other and both use
static construction have no valid static construction order.
One reason, I think, why the spec states that is because in
theory it would not always be possible for the compiler to
decide the order, e.g. when executing them changes the
("shared") execution environment's state:
---
module a;
import b;
static this()
{
// Does something to the OS state
syscall_a();
}
---
---
module b;
import a;
static this()
{
// Also does something to the OS state
syscall_b();
}
---
The "fix" as I see it would be to either not use static
construction in modules that import each other, or propose a
set of rules for the spec that define a always solvable subset
for the compiler.
[1] https://dlang.org/spec/module.html#order_of_static_ctor
The compiler shouldn't arbitrarily force one to make arbitrary
decisions that waste time and money.
My apologies, I confused compiler and runtime when writing that
reply (the detection algorithm resulting in your crash is built
into druntime).
The runtime, however, is compliant with the spec on this AFAICT.
The compiler should only run the static this's once per module
load anyways, right?
Static module constructors are run once per module per thread [1]
(if you want once per module you need shared static module
constructors).
If it is such a problem then some way around it should be
included: @force static this() { } ?
The only current workaround is what Biotronic mentioned: You can
customize the druntime cycle detection via the --DRT-oncycle
command line option [2].
The compiler shouldn't make assumptions about the code I write
and always choose the worse case, it becomes an unfriendly
relationship at that point.
If your point remains when replacing 'compiler' with 'runtime':
It makes no assumptions in the case you described, it enforces
the language specification.
[1] https://dlang.org/spec/module.html#staticorder
[2] https://dlang.org/spec/module.html#override_cycle_abort
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 10:08:11 UTC, Moritz Maxeiner
wrote:
On Tuesday, 12 September 2017 at 09:11:20 UTC, Joseph wrote:
I have two nearly duplicate files I added a static this() to
initialize some static members of an interface.
On one file when I add an empty static this() it crashes while
the other one does not.
The exception that happens is
Cyclic dependency between module A and B.
Why does this occur on an empty static this? Is it being ran
twice or something? Anyway to fix this?
The compiler errors because the spec states [1]
Each module is assumed to depend on any imported modules
being statically constructed first
, which means two modules that import each other and both use
static construction have no valid static construction order.
One reason, I think, why the spec states that is because in
theory it would not always be possible for the compiler to
decide the order, e.g. when executing them changes the
("shared") execution environment's state:
---
module a;
import b;
static this()
{
// Does something to the OS state
syscall_a();
}
---
---
module b;
import a;
static this()
{
// Also does something to the OS state
syscall_b();
}
---
The "fix" as I see it would be to either not use static
construction in modules that import each other, or propose a
set of rules for the spec that define a always solvable subset
for the compiler.
[1] https://dlang.org/spec/module.html#order_of_static_ctor
The compiler shouldn't arbitrarily force one to make arbitrary
decisions that waste time and money.
My solution was to turn those static this's in to functions and
simply call them at at the start of main(). Same effect yet
doesn't crash. The compiler should only run the static this's
once per module load anyways, right? If it is such a problem then
some way around it should be included: @force static this() { } ?
The compiler shouldn't make assumptions about the code I write
and always choose the worse case, it becomes an unfriendly
relationship at that point.
Re: Adding empty static this() causes exception
The simplest example of a cycle is probably this:
module A;
import B;
int n1 = 17;
static this() {
n1 = n2;
}
//
module B;
import A;
int n2 = 42;
static this() {
n2 = n1;
}
What's the value of n1 and n2 after module constructors are run?
Since both module constructors can run arbitrary code, it's
impossible to prove in the general case whether one of them
depends on the other.
--
Biotronic
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 09:11:20 UTC, Joseph wrote:
I have two nearly duplicate files I added a static this() to
initialize some static members of an interface.
On one file when I add an empty static this() it crashes while
the other one does not.
The exception that happens is
Cyclic dependency between module A and B.
Why does this occur on an empty static this? Is it being ran
twice or something? Anyway to fix this?
Seriously, simply adding static this() { } to module B crashes
the program ;/ module A and module B both import each other
because there are types that they need to share but that is
all(one uses an enum of the other and vice versa).
https://dlang.org/spec/module.html#order_of_static_ctor
"Cycles (circular dependencies) in the import declarations are
allowed as long as not both of the modules contain static
constructors or static destructors. Violation of this rule will
result in a runtime exception."
So if you have a static this() in both A and B, and A imports B
and B imports A, you will get this error message. You can pass
--DRT-oncycle=ignore to the program to hide the problem, but a
better solution is to find a way to live with fewer static
this()s.
The reason this exception is thrown is that one module's static
this() might otherwise depend on another module's static this
that depends on the first module again, and there is no good way
to check if it actually depends or just potentially.
--
Biotronic
Re: Adding empty static this() causes exception
On Tuesday, 12 September 2017 at 09:11:20 UTC, Joseph wrote:
I have two nearly duplicate files I added a static this() to
initialize some static members of an interface.
On one file when I add an empty static this() it crashes while
the other one does not.
The exception that happens is
Cyclic dependency between module A and B.
Why does this occur on an empty static this? Is it being ran
twice or something? Anyway to fix this?
The compiler errors because the spec states [1]
Each module is assumed to depend on any imported modules being
statically constructed first
, which means two modules that import each other and both use
static construction have no valid static construction order.
One reason, I think, why the spec states that is because in
theory it would not always be possible for the compiler to decide
the order, e.g. when executing them changes the ("shared")
execution environment's state:
---
module a;
import b;
static this()
{
// Does something to the OS state
syscall_a();
}
---
---
module b;
import a;
static this()
{
// Also does something to the OS state
syscall_b();
}
---
The "fix" as I see it would be to either not use static
construction in modules that import each other, or propose a set
of rules for the spec that define a always solvable subset for
the compiler.
[1] https://dlang.org/spec/module.html#order_of_static_ctor
Adding empty static this() causes exception
I have two nearly duplicate files I added a static this() to
initialize some static members of an interface.
On one file when I add an empty static this() it crashes while
the other one does not.
The exception that happens is
Cyclic dependency between module A and B.
Why does this occur on an empty static this? Is it being ran
twice or something? Anyway to fix this?
Seriously, simply adding static this() { } to module B crashes
the program ;/ module A and module B both import each other
because there are types that they need to share but that is
all(one uses an enum of the other and vice versa).
