Static method for struct ?

[ken0x0a]

I want static method for struct

It might make json handling easier.
Currently, decoding json is depending on compiler, and x.json2 module requires all fields to be mut.

(It's the same content with #7610 (comment))

Static method for struct is something like followings.

enum DataType {
	str
	int_
	obj
	unknown
}
struct BaseResponse {
	typ DataType [json: @type]
	inner InnerResponse
}
struct InnerResponse {
	some string
	thing int
	important bool
}

interface Decoder<T> {
	from_json(j json2.Any) T // maybe `static from_json(j json2.Any) T` ?
}
fn decode_json<T>(src string) {
	j := json2.raw_decode(src)
	return T.from_json(j)
}
fn from_any<T>(j json2.Any) {
	return T.from_json(j)
}

fn DataType.from_json(j json2.Any) DataType {
	str := j.str()
	return match str {
		'string' { .str }
		'int', 'integer' { .int_ }
		'obj' { .obj }
		else { .unknown }
	}
}
fn BaseResponse.from_json(j json2.Any) BaseResponse {
	obj := j.as_map()
	return BaseResponse {
		inner: from_any<InnerResponse>(obj['inner'])
		typ: from_any<DataType>(obj['inner'])
	}
}

Syntax can be anything.

fn BaseResponse.from_json(j json2.Any) BaseResponse { ... } 

or maybe

fn BaseResponse::from_json(j json2.Any) BaseResponse { ... } 

[ken0x0a]

Now I'm creating precompile code generation script using v.ast & v.fmt.

And I'm using x.json2 module but it requires all fields to be mut.
And also, there might be some bug (#11531) and I cannot implement nicely.

[ken0x0a]

https://github.com/ken0x0a/v_derive

Generated file is very ugly without static method.

[igotfr]

can be used for constructors

struct Name {
  field1 int
  field2 string
}

// special syntax for constructors
fn Name.field1(field1 int) Name {
  return Name {
    field1: field1
    field2: 'default'
  }
}

fn main() {
  n := Name.field1(7)
}

[yashsamit]

@medvednikov This is a must feature. Any timeline estimate?

[yashsamit]

//THIS is not POSSIBLE
pub struct Margin {
    top f64
    right f64
    bottom f64
    left f64
}

// if the static method allowed 
pub fn new()  Margin {}

pub type Padding = Margin
pub type Rect = Margin

Padding::new()
Margin::new()
Rect::new()


// Alternate seems ugly
// We have to add new_margin() and use the same fn for other types or create many new variants. 
// It becomes ugly when we have other constructors also like 
from_vals(a, b, c, d) 
from_val(a)

//etc

We can't name the module in any file because it is based on dir. I have all files inside types dir.
If the custom name of the module is allowed then it will very neat and clean.

It will like

//margin and padding are module names
margin.new()
padding.new()

//Right now to achieve this, I have to create 4 folders for small files. 

In the doc, it mentioned that v is very modular. I feel without a filename based module name, it's not that much modular.

Solutions:

• Support custom module name based on file but not folder.
• Add support Static method for struct ? #11532
• Constructor support.

[spytheman]

V now has static methods (for all types, not just structs):

struct Abc { x int }
fn Abc.new() Abc { return Abc{ x: 42 } }
dump( Abc.new() )

produces now:

[a.v:3] Abc.new(): Abc{
    x: 42
}