Generics implementation maybe keeps state from previous run, that it should have reset

[blackshirt]

Describe the bug

Code: https://play.vlang.io/p/7e39789b29

struct Parser {
mut:
	data []u8
}

fn (mut p Parser) read_element[T]() !T {
	t := T.parse(mut p)!
	return t
}

struct TestA {
	data []u8
}

fn TestA.parse(mut p Parser) !TestA {
	return TestA{
		data: p.data
	}
}

struct TestB {
	st string
}

fn TestB.parse(mut p Parser) !TestB {
	return TestB{
		st: p.data.hex()
	}
}

fn main() {
	data := []u8{len: 5, init: u8(5)}
	mut p := Parser{
		data: data
	}

	ta := p.read_element[TestA]()!
	dump(ta)

	tb := p.read_element[TestB]()!
	dump(tb)
}

Reproduction Steps

Run the code on the above playground link or below

Expected Behavior

[code.v:38] ta: TestA{
    data: [5, 5, 5, 5, 5]
}
[code.v:41] tb: TestB{
    st: '0505050505'
}

Current Behavior

Output:

code.v:8:2: error: `TestA` doesn't implement method `msg` of interface `IError`
    6 | fn (mut p Parser) read_element[T]() !T {
    7 |     t := T.parse(mut p)!
    8 |     return t
      |     ~~~~~~~~
    9 | }
   10 |
code.v:8:2: error: `TestA` doesn't implement method `code` of interface `IError`
    6 | fn (mut p Parser) read_element[T]() !T {
    7 |     t := T.parse(mut p)!
    8 |     return t
      |     ~~~~~~~~
    9 | }
   10 |
code.v:8:9: error: cannot use `TestA` as type `!TestB` in return argument
    6 | fn (mut p Parser) read_element[T]() !T {
    7 |     t := T.parse(mut p)!
    8 |     return t
      |            ^
    9 | }
   10 |
Exited with error status 1

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.8 897ec51.ee3a182

Environment details (OS name and version, etc.)

V full version: V 0.4.8 897ec51.ee3a182
OS: linux, Debian GNU/Linux 12 (bookworm) (VM)
Processor: 2 cpus, 64bit, little endian, Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz

getwd: /home/admin/playground
vexe: /home/admin/v/v
vexe mtime: 2024-11-14 06:25:27

vroot: OK, value: /home/admin/v
VMODULES: OK, value: .vmodules
VTMP: OK, value: /tmp/v_0

Git version: git version 2.39.5
Git vroot status: Error: fatal: detected dubious ownership in repository at '/home/admin/v'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/admin/v
.git/config present: true

CC version: cc (Debian 12.2.0-14) 12.2.0
emcc version: N/A
thirdparty/tcc status: Error: fatal: detected dubious ownership in repository at '/home/admin/v/thirdparty/tcc'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/admin/v/thirdparty/tcc
 Error: fatal: detected dubious ownership in repository at '/home/admin/v/thirdparty/tcc'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/admin/v/thirdparty/tcc

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_{Huly®: V_0.6-21300}

[jorgeluismireles]

I think you can use an interface without handling any error:

interface Parser {
mut:
	parse_data(data []u8)
}

struct ParserA implements Parser {
mut:
	data []u8
}	

fn (mut p ParserA) parse_data(data []u8) {
	p.data = data.clone()
}

struct ParserB implements Parser {
mut:
	data string	
}

fn (mut p ParserB) parse_data(data []u8) {
	p.data = data.hex()
}

fn main() {
	data := [u8(5), 5, 5, 5]
	mut pa := ParserA{}
	mut pb := ParserB{}
	pa.parse_data(data)
	pb.parse_data(data)
	assert pa.data == [u8(5),5,5,5]
	assert pb.data == '05050505'
}

https://play.vlang.io/p/055efba784

[blackshirt]

Thanks...I think its different use case.
Your snippet works without generic, the problem maybe arises when its work with generic like above snippet.