digitalmars.D.bugs - [Issue 9100] New: Weird behavior on template instance argument
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http://d.puremagic.com/issues/show_bug.cgi?id=9100
Summary: Weird behavior on template instance argument
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: k.hara.pg gmail.com
On template instance argument, a template arguments *sometimes* is treated just
as a symbol.
That looks weird and inconsistent behavior.
----
template Id(alias A) { alias Id = A; } // L1
template ErrId(alias A) { static assert(0); }
template TypeTuple(TL...) { alias TypeTuple = TL; }
class C {
void fun(){}
void tfun(T)(){}
TypeTuple!(int, long) field; // L7
void test()
{
auto c = this;
alias t1a = Id!(c.fun); // OK
alias t1b = Id!(this.fun); // Weird error, bad
// test1.d(1): Error: variable test1.A type void is inferred
// from initializer this.fun(), and variables cannot be of type void
// -> internally given DotVarExp
alias t2a = Id!(c.tfun); // OK
alias t2b = ErrId!(this.tfun); // No error occurs, why?
// -> internally given DotTemplateExp
alias t3a = Id!(foo); // OK
alias t3b = Id!(mixin("foo")); // Prints weird error, bad
// test1.d(1): Error: variable test1.A type void is inferred
// from initializer foo(), and variables cannot be of type void
// -> internally given TemplateExp
alias t4b = TypeTuple!(field); // L28, NG
// test1.d(7): Error: expression this._field_field_0 is not a valid
template value argument
// test1.d(7): Error: expression this._field_field_1 is not a valid
template value argument
// test1.d(28): Error: template instance
test1.TypeTuple!(this._field_field_0, this._field_field_1) error instantiating
alias t4a = TypeTuple!(GetField!0); // L32, NG
// test1.d(42): Error: alias test1.GetField!(0).GetField cannot alias an
expression _field_field_0
// test1.d(42): Error: alias test1.GetField!(0).GetField cannot alias an
expression _field_field_0
// test1.d(32): Error: template instance test1.GetField!(0) error
instantiating
// test1.d(42): Error: alias test1.GetField!(0).GetField cannot alias an
expression _field_field_0
// test1.d(32): Error: C.field[0u] is not a type
}
}
void foo()(){}
template GetField(size_t i) { alias GetField = C.field[i]; } // L42
void main(){ (new C()).test(); }
----
From the internal of dmd implementation, if failure to give just as a symbol,
the argument has been semantically analysed as an expression which refers a
symbol - DotVarExp, TemplateExp, and DotTemplteExp.
D does not support an aliasing of expression, so I think these *expression
template arguments* should be deduced to just a symbol. In such deduction, the
*context* expression for the symbol (e1, in DotVarExp or DotTemplateExp) should
be just removed.
It will increase consistency and will relax some limitations.
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This is a root cause of some 2.061head regressions - bug 9091, bug 8972, and
bug 8971.
If you use __traits() to get member symbol inside class/struct member function,
the found member symbol will have the implicit 'this'.
Passing the __traits result to the template argument will caught the *bug*
which I explained here.
class C {
int var;
void test() {
__traits(getMember, C, "var"); // same as this.var -> DotVarExp
alias t = Id!(__traits(getMember, C, "var")); // same as Id!(this.var),
hit!
}
}
void main() {
__traits(getMember, C, "var") // same as C.var == Just a symbol
alias t = Id!(__traits(getMember, C, "var")); // same as Id!(C.var), no
problem
}
Therefore, I think this is an important semantic analysis bug which should be
fixed.
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As a related note, this program runs successfully with no error in current
compiler.
It looks weird, but is expected from the view of language consistency.
void main(){ (new C(1)).test(); }
template Id(alias A) { alias Id = A; }
class C
{
int n;
this(int x){ n = x; }
int fun(){ return n; }
void test()
{
auto c = new C(2);
assert(c.fun() == 2);
alias f = Id!(c.fun);
assert(f() == 1); // calls this.fun, not c.fun
}
}
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Kenji Hara <k.hara.pg gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |pull, rejects-valid
Blocks| |9091, 9083
Severity|normal |major
https://github.com/D-Programming-Language/dmd/pull/1340
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Kenji Hara <k.hara.pg gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |8972, 8971
The following bugs that were already fixed are fundamentally dependent on this.
Issue 8971 - __traits(getOverloads) fails in a member function
Issue 8972 - __traits fails in a struct member function
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http://d.puremagic.com/issues/show_bug.cgi?id=9100 Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/1ba96f16d5c0300f4de8f4d2d851d65cf269dd15 fix Issue 9100 - Weird behavior on template instance argument https://github.com/D-Programming-Language/dmd/commit/2f043f66b50a5f7d505cf9776a8ca2bfd632cabd Issue 9100 - Weird behavior on template instance argument -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 09 2012
http://d.puremagic.com/issues/show_bug.cgi?id=9100
timon.gehr gmx.ch changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |timon.gehr gmx.ch
As a related note, this program runs successfully with no error in current
compiler.
It looks weird, but is expected from the view of language consistency.
void main(){ (new C(1)).test(); }
template Id(alias A) { alias Id = A; }
class C
{
int n;
this(int x){ n = x; }
int fun(){ return n; }
void test()
{
auto c = new C(2);
assert(c.fun() == 2);
alias f = Id!(c.fun);
assert(f() == 1); // calls this.fun, not c.fun
}
}
Language _sanity_ is what is important. It should call c.fun or be a compile
time error. Deliberately assigning unsupported code strange semantics in order
to be consistent with existing buggy compiler behaviour just makes it harder to
lift restrictions later.
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Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |bugzilla digitalmars.com
Resolution| |FIXED
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