match []u8 gives &[]u8

[einar-hjortdal]

Describe the bug

In the code here the compiler gives me the following error:

src/protocol.v:472:33: error: cannot use `&[]u8` as `[]u8` in argument 1 to `bytes_to_blr`
  470 |             []u8 {
  471 |                 if param.len < max_char_length {
  472 |                     blr, value := bytes_to_blr(param)
      |                                                ~~~~~
  473 |                     _ := b.write(blr) or { 0 } // does not return any error
  474 |                     _ := v.write(value) or { 0 } // does not return any error

But the type matched []u8, why am I getting &[]u8?

Reproduction Steps

attempt to compile the linked repo

Expected Behavior

no error

Current Behavior

error

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.10 e491eb0

Environment details (OS name and version, etc.)

|V full version      |V 0.4.10 537605a.e491eb0
|:-------------------|:-------------------
|OS                  |linux, "openmamba release 2024.6 for x86_64 (rolling)"
|Processor           |8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz
|Memory              |11.83GB/31.16GB
|                    |
|V executable        |/home/einar/.local/lib64/v/v
|V last modified time|2025-03-26 15:49:42
|                    |
|V home dir          |OK, value: /home/einar/.local/lib64/v
|VMODULES            |OK, value: /home/einar/.vmodules
|VTMP                |OK, value: /tmp/v_1000
|Current working dir |OK, value: /home/einar/Documents/projects/vlang/active/firebird
|                    |
|Git version         |git version 2.49.0
|V git status        |weekly.2025.13-16-ge491eb05
|.git/config present |true
|                    |
|cc version          |cc (GCC) 14.2.1 20240909
|gcc version         |gcc (GCC) 14.2.1 20240909
|clang version       |N/A
|tcc version         |tcc version 0.9.28rc 2024-07-31 HEAD@1cee0908 (x86_64 Linux)
|tcc git status      |thirdparty-linux-amd64 0134e9b9
|emcc version        |N/A
|glibc version       |ldd (GNU libc) 2.41

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[huly-for-github]

Connected to Huly®: V_0.6-22445

[jorgeluismireles]

I tested this oversimplification of your code in the playground compiles ok:

type Value = string | []u8

fn bytes_to_blr(bytes []u8) {
	println('${bytes}')
}

fn params_to_blr(params []Value) {
	for i := 0; i < params.len; i++ {
		param := params[i]
		match param {
			string {
				bytes_to_blr(param.bytes())			
			}
			[]u8 {
				bytes_to_blr(param)
			}
		}
	}
}

I didn't check your Value sum type details nor your bytes_to_blr arguments though.

[felipensp]

I tested this oversimplification of your code in the playground compiles ok:

type Value = string | []u8

fn bytes_to_blr(bytes []u8) {
println('${bytes}')
}

fn params_to_blr(params []Value) {
for i := 0; i < params.len; i++ {
param := params[i]
match param {
string {
bytes_to_blr(param.bytes())
}
[]u8 {
bytes_to_blr(param)
}
}
}
}
I didn't check your Value sum type details nor your bytes_to_blr arguments though.

This is because Value is not a sumtype, but an empty interface. interface Value {}

[felipensp]

Since it is an interface one, use bytes_to_blr(*param) @einar-hjortdal

[einar-hjortdal]

Is there a reason why this happens, and why does the compiler error with []u8 and not with other types?

[einar-hjortdal]

I tested this oversimplification of your code in the playground compiles ok:

You are correct, this does not happen with sum types.