Invariant not called from autogenerated class/struct constructor/destructor

[burner]

matti.niemenmaa+dbugzilla reported this on 2006-11-15T07:34:26Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=519

CC List

• alex (alexrp)
• andrei (andralex)
• bearophile_hugs
• code (MartinNowak)
• devbai
• gim913
• k.hara.pg
• qs.il.paperinik
• smjg
• verylonglogin.reg
• yebblies

Description

This code should fail regardless of whether the constructor is commented out or not:

class Foo { // this() {} invariant { assert (false); } }

void main() { Foo foo = new Foo(); }

Yet, it only does if the constructor is explicitly specified. The invariant is not called from the automatically inserted constructor, even though there's no reason why it shouldn't be.

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smjg commented on 2009-01-10T11:30:46Z

Bug 2184 has been marked as a duplicate of this bug.

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bearophile_hugs commented on 2010-06-17T13:08:26Z

Issue 4331 has been marked as a duplicate of this issue.

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andrei (@andralex) commented on 2010-11-26T11:39:12Z

The example needs parens:

class Foo { // this() {} invariant { assert (false); } }

void main() { Foo foo = new Foo(); }

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andrei (@andralex) commented on 2010-11-26T11:39:39Z

Forgot to add the actual parens :o).

class Foo { // this() {} invariant() { assert (false); } }

void main() { Foo foo = new Foo(); }

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yebblies commented on 2011-06-17T07:53:50Z

What should happen in these cases?

class A { shared invariant {} }

class A { immutable invariant {} }

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k.hara.pg commented on 2011-06-20T05:45:02Z

Autogenerated destructor has same problem:

import core.stdc.stdio : printf; class Foo { invariant() { printf("Foo.invariant\n"); } } void main() { Foo foo = new Foo(); printf("lifetime of foo\n"); delete foo; }

Should print:

Foo.invariant lifetime of foo Foo.invariant

But current output is:

lifetime of foo

[burner]

yebblies commented on 2012-01-21T17:21:31Z

Issue 7334 has been marked as a duplicate of this issue.

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verylonglogin.reg commented on 2012-10-30T06:05:58Z

Structs have the same problem:

import std.stdio;

struct S { invariant() { writeln("invariant"); } // never called // ~this() { writeln("~this"); } // uncomment to call invariant }

void main() { auto s = S(); }

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clugdbug commented on 2012-11-15T00:20:52Z

Issue 9019 has been marked as a duplicate of this issue.

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bearophile_hugs commented on 2013-02-06T03:19:45Z

See also Issue 9454

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bugzilla (@WalterBright) commented on 2014-11-11T21:11:29Z

I agree that the invariant should run on non-empty struct literals and on destruction.

I'm skeptical, however, of the value of running it on default construction, as those values will always be the .init ones.

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bugzilla (@WalterBright) commented on 2014-11-12T01:04:15Z

https://github.com/D-Programming-Language/dmd/pull/4136

(But does not do invariant call for default construction, will change spec to say that isn't don't.)

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bugzilla (@WalterBright) commented on 2014-11-12T01:47:00Z

Documentation fix:

https://github.com/D-Programming-Language/dlang.org/pull/699

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code (@MartinNowak) commented on 2014-11-18T18:20:48Z

Rainer raised an important question for running invariant before class destruction. Because GC finalization order is undetermined an invariant that would check whether some classes's field points to a valid instance could fail because the pointed-to class could already have been finalized.

http://forum.dlang.org/post/m4eu6v$trq$1@digitalmars.com

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smjg commented on 2014-11-22T02:02:01Z

(In reply to Walter Bright from comment #11)

I'm skeptical, however, of the value of running it on default construction, as those values will always be the .init ones.

Maybe have a rule that, if the -unittest option is set, autogenerate a unittest to call the invariant on the .init.

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andrei (@andralex) commented on 2015-01-14T23:43:37Z

I stated this elsewhere, just making sure I don't forget: probably we don't want to invoke invariants during the GC cycle.

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code (@MartinNowak) commented on 2015-01-15T10:18:44Z

(In reply to Andrei Alexandrescu from comment #16)

I stated this elsewhere, just making sure I don't forget: probably we don't want to invoke invariants during the GC cycle.

Walter has a different opinion on this, I don't follow his argument though. http://forum.dlang.org/post/m753hk$pt2$1@digitalmars.com

Currently it can't be done, because the calls to the invariant are embedded into the generated destructor function.

Also the invariant is called twice, before and after running the destructor. The latter forces one to perform additional cleanup, e.g. setting pointers to null.

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andrei (@andralex) commented on 2015-01-15T16:03:23Z

(In reply to Martin Nowak from comment #17)

(In reply to Andrei Alexandrescu from comment #16)

I stated this elsewhere, just making sure I don't forget: probably we don't want to invoke invariants during the GC cycle.

Walter has a different opinion on this, I don't follow his argument though. http://forum.dlang.org/post/m753hk$pt2$1@digitalmars.com

Currently it can't be done, because the calls to the invariant are embedded into the generated destructor function.

Well a simple invariant would be:

assert(this.parent.child is this);

which would be placed in some child node, or could be moved in parent like this:

assert(this.child.parent is this);

The invariant involves two objects no matter where you put it.

Also the invariant is called twice, before and after running the destructor. The latter forces one to perform additional cleanup, e.g. setting pointers to null.

That's definitely a problem. Invariants are not supposed to hold after destruction.

[burner]

bugzilla (@WalterBright) commented on 2018-02-09T05:00:19Z

Rebooted as: https://github.com/dlang/dmd/pull/7536/

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dlang-bot commented on 2019-06-12T11:01:19Z

@RazvanN7 created dlang/dmd pull request #10022 "Fix Issue 519 - Invariant not called from autogenerated class/struct constructor/destructor" fixing this issue:

• Fix Issue 519 - Invariant not called from autogenerated class/struct constructor/destructor

https://github.com/dlang/dmd/pull/10022

[burner]

qs.il.paperinik commented on 2023-01-13T16:38:49Z

Maybe this can be done via a caller-side lowering:

The expression T(args...) would become

{
    auto result = T(args...);
    assert(() @trusted { return &result; }());
    return result;
}()

The @trusted block is to be able to take the address without dip1000.