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digitalmars.D - Help needed for "recursive template expansion error"

reply Anthony Abeo <anthonyabeo gmail.com> writes:
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.
Oct 21 2019
parent reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
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);
Oct 21 2019
parent reply Anthony Abeo <anthonyabeo gmail.com> writes:
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.
Oct 22 2019
parent reply Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
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
Oct 22 2019
parent Anthony Abeo <anthonyabeo gmail.com> writes:
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.
Oct 23 2019