Passing a map to a generic argument changes a key value from int to an empty string

[prantlf]

Describe the bug

1. Let this map: { 'a': 1 }
2. Enter the method marshal
3. Which calls the method marshal_map
4. And see it received as { 'a': '' }

This is simplified code. Runnable file is further below.

fn marshal[T](val T) {
  // received { 'a': 1 }
  marshal_map(val)
}

fn marshal_map[T](val map[string]T) {
  // received { 'a': '' }
}

marshal({ 'a': 1 })

Apparently, the value map[string]int was passed as map[string]string from marshal to marshal_map and the value of the key 'a' became the default value for string - ''.

Reproduction Steps

1. Save the code below to the file marshal_test.v
2. Run the command v marshal_test.v.
3. Observe the following output:

test_marshal
 marshal: {'a': 1}
 marshal_map: {'a': ''}
test_marshal_map
 marshal_map: {'a': 1}

When marshal_map[T](val map[string]T) is called directly, the input map enters it correctly as map[string]int.

When marshal_map[T](val map[string]T) is called from marshal[T](val T), the input map enters it wrong as map[string]string.

The code of marshal_test.v, which is very simplified from a JSON parser and formatter:

module json

fn marshal[T](val T) {
	println(' marshal: ${val}')
	assert val['a'] == 1
	marshal_map(val)
}

fn marshal_map[T](val map[string]T) {
	println(' marshal_map: ${val}')
	// assert val['a'] == 1
}

fn test_marshal() {
	println('test_marshal')
	marshal({
		'a': 1
	})
}

fn test_marshal_map() {
	println('test_marshal_map')
	marshal_map({
		'a': 1
	})
}

Expected Behavior

When marshal_map[T](val map[string]T) is called from marshal[T](val T) with an input parameter of the type map[string]int, this type will be passed properly via marshal to marshal_map and the value of the key 'a' will be 1.

Current Behavior

I guess that map[string]int was converted to map[string]string and all key values were replaced by strings with default string values - ''.

Possible Solution

I wish I knew :-)

Additional Information/Context

When enabling the commented out assert in marshal_map:

`fn marshal_map[T](val map[string]T) {
	println(' marshal_map: ${val}')
	assert val['a'] == 1
}

The compiler fails with a complaint that the right argument was supposed to be a string, as expected from my assumption above:

marshal_test.v:11:12: error: infix expr: cannot use `int literal` (right expression) as `string`
    9 | fn marshal_map[T](val map[string]T) {
   10 |     println(' marshal_map: ${val}')
   11 |     assert val['a'] == 1
      |               ~~~~~~~~~~
   12 | }
   13 |

However, when changing the argument from 1 to '1':

fn marshal_map[T](val map[string]T) {
	println(' marshal_map: ${val}')
	assert val['a'] == '1'
}

The compiler fails again, now desiring an integer:

❯ v marshal_test.v
marshal_test.v:11:12: error: infix expr: cannot use `string` (right expression) as `int`
    9 | fn marshal_map[T](val map[string]T) {
   10 |     println(' marshal_map: ${val}')
   11 |     assert val['a'] == '1'
      |               ~~~~~~~~~~~~
   12 | }
   13 |

It doesn't know what it wants :-)

V version

V 0.4.7 ddb6685

Environment details (OS name and version, etc.)

V full version: V 0.4.7 ddb6685
OS: macos, macOS, 14.5, 23F79
Processor: 12 cpus, 64bit, little endian, Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz

getwd: /Users/ferdipr/Sources/github/v-bug
vexe: /Users/ferdipr/.vup/weekly.2024.32/v
vexe mtime: 2024-08-06 07:59:48

vroot: OK, value: /Users/ferdipr/.vup/weekly.2024.32
VMODULES: OK, value: /Users/ferdipr/.vmodules
VTMP: OK, value: /tmp/v_501

Git version: git version 2.46.0
Git vroot status: Error: fatal: not a git repository (or any of the parent directories): .git
.git/config present: false

CC version: Apple clang version 15.0.0 (clang-1500.3.9.4)
thirdparty/tcc: N/A

Note

You can use the 👍 reaction to increase the issue's priority for developers.

Please note that only the 👍 reaction to the issue itself counts as a vote.
Other reactions and those to comments will not be taken into account.

[Cergoo]

generics it is a very important thing to a lang.
It need to be worked out well, in theory it is just templates