Hello all,

I have an Algebraic type of structs as shown below. One of the structs is the `Code` struct and this struct holds an array of ATTR_INFO. It is self-referential. Obviously the compiler is unable to get the maximum size of ATTR_INFO at compile-time, hence throwing the error. I will be very grateful for any help to resolve this issue.

alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue, Excepsion, Code,
                                                    LineNumberTable, LocalVariableTable);

struct Code
{
	size_t attribute_name_index;
	size_t attribute_len;
	size_t max_stack;
	size_t max_locals;
	size_t code_length;
	const(ubyte[]) code;
	size_t exception_table_length;
	Tuple!(size_t, size_t, size_t, size_t) exception_table;
	size_t attribute_count;
	ATTR_INFO[] attributes;
}

STACK TRACE
/Library/D/dmd/src/phobos/std/variant.d(1517,23): Error: template instance `VariantN!(maxSize!(SourceFile, ConstantV
alue, Excepsion, Code, LineNumberTable, LocalVariableTable), T)` recursive template expansion
/Library/D/dmd/src/phobos/std/variant.d(87,48): Error: template instance `std.variant.maxSize!(Code, LineNumberTable
, LocalVariableTable)` error instantiating
/Library/D/dmd/src/phobos/std/variant.d(87,48):        instantiated from here: maxSize!(Excepsion, Code, LineNumberT
able, LocalVariableTable)
/Library/D/dmd/src/phobos/std/variant.d(87,48):        instantiated from here: maxSize!(ConstantValue, Excepsion, Code, LineNumberTable, LocalVariableTable)
/Library/D/dmd/src/phobos/std/variant.d(1517,33):        instantiated from here: maxSize!(SourceFile, ConstantValue, Excepsion, Code, LineNumberTable, LocalVariableTable)
source/app.d(8,19):        instantiated from here: Algebraic!(SourceFile, ConstantValue, Excepsion, Code, LineNumberTable, LocalVariableTable)
/Library/D/dmd/bin/dmd failed with exit code 1.

On Monday, 21 October 2019 at 18:14:11 UTC, Anthony Abeo wrote:
> Hello all,
>
> I have an Algebraic type of structs as shown below. One of the structs is the `Code` struct and this struct holds an array of ATTR_INFO. It is self-referential. Obviously the compiler is unable to get the maximum size of ATTR_INFO at compile-time, hence throwing the error. I will be very grateful for any help to resolve this issue.
>
> alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue, Excepsion, Code,
>                                                     LineNumberTable, LocalVariableTable);
>
> struct Code
> {
> 	size_t attribute_name_index;
> 	size_t attribute_len;
> 	size_t max_stack;
> 	size_t max_locals;
> 	size_t code_length;
> 	const(ubyte[]) code;
> 	size_t exception_table_length;
> 	Tuple!(size_t, size_t, size_t, size_t) exception_table;
> 	size_t attribute_count;
> 	ATTR_INFO[] attributes;
> }

Please post such questions to the learn forum in the future.

One way to fix this is to use the `This` type to perform type substitution in the Algebraic which refers to the final type of the Algebraic, used like `alias F = Algebraic!(int, string, This[])`.  Where F is either an int, a string or an array of Fs.

You could probably remove `attributes` from code and use

alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue,  Excepsion, Tuple!(Code,This[]), LineNumberTable, LocalVariableTable);

On Monday, 21 October 2019 at 18:45:44 UTC, Nicholas Wilson wrote:
> On Monday, 21 October 2019 at 18:14:11 UTC, Anthony Abeo wrote:
>> [...]
>
> Please post such questions to the learn forum in the future.
>
> One way to fix this is to use the `This` type to perform type substitution in the Algebraic which refers to the final type of the Algebraic, used like `alias F = Algebraic!(int, string, This[])`.  Where F is either an int, a string or an array of Fs.
>
> You could probably remove `attributes` from code and use
>
> alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue,  Excepsion, Tuple!(Code,This[]), LineNumberTable, LocalVariableTable);

- Please post such questions to the learn forum in the future.
Noted. I will do that next time.

I tried your suggestion and it fails silently; no error message / stack trace.

On Tuesday, 22 October 2019 at 08:16:47 UTC, Anthony Abeo wrote:
> On Monday, 21 October 2019 at 18:45:44 UTC, Nicholas Wilson wrote:
>> On Monday, 21 October 2019 at 18:14:11 UTC, Anthony Abeo wrote:
>>> [...]
>>
>> Please post such questions to the learn forum in the future.
>>
>> One way to fix this is to use the `This` type to perform type substitution in the Algebraic which refers to the final type of the Algebraic, used like `alias F = Algebraic!(int, string, This[])`.  Where F is either an int, a string or an array of Fs.
>>
>> You could probably remove `attributes` from code and use
>>
>> alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue,  Excepsion, Tuple!(Code,This[]), LineNumberTable, LocalVariableTable);
>
> - Please post such questions to the learn forum in the future.
> Noted. I will do that next time.
>
> I tried your suggestion and it fails silently; no error message / stack trace.

I'd suggest using SumType (https://code.dlang.org/packages/sumtype) instead of std.variant, as the latter has its share of problems.

Otherwise, this kinda works, but can hardly be called anything but a horrible hack:

alias ATTR_INFO = Algebraic!(SourceFile, ConstantValue, Excepsion, Code,
                             LineNumberTable, LocalVariableTable);

struct Code
{
	size_t attribute_name_index;
	size_t attribute_len;
	size_t max_stack;
	size_t max_locals;
	size_t code_length;
	const(ubyte[]) code;
	size_t exception_table_length;
	Tuple!(size_t, size_t, size_t, size_t) exception_table;
	size_t attribute_count;
	private ubyte[] _attributes;
}

ref ATTR_INFO[] attributes(return ref Code code)
{
    return *cast(ATTR_INFO[]*)&code._attributes;
}

It will need some fixing if you have any destructors, as Code treats those ATTR_INFOs as just a bunch of bytes, but it will make the code compile and it might be good enough. Seriously though, check out SumType instead.

--
  Simen

On Tuesday, 22 October 2019 at 08:42:48 UTC, Simen Kjærås wrote:
> On Tuesday, 22 October 2019 at 08:16:47 UTC, Anthony Abeo wrote:
>> [...]
>
> I'd suggest using SumType (https://code.dlang.org/packages/sumtype) instead of std.variant, as the latter has its share of problems.
>
> [...]

Thanks Simen.

the sumtype package helped.

Thanks everyone.