Allow anonymous structures to be created on the fly

[gchumillas]

Describe the feature

Currently you can create "nested" anonymous structures:
https://docs.vlang.io/structs.html#anonymous-structs

Use Case

But you can't create anonymous structures on the fly:

// this code doesn't compile:
book := struct {
	title: 'Allice in Wornderland'
	year: 1865
}

Proposed Solution

Allow to create not only nested anonymous structures but also top-level anonymous structures.

Other Information

V Playground: https://play.vlang.io/p/e7ad7d9486

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.9 a59ebea

Environment details (OS name and version, etc.)

|V full version      |V 0.4.9 a59ebea
|:-------------------|:-------------------
|OS                  |linux, Debian GNU/Linux 12 (bookworm) (VM)
|Processor           |2 cpus, 64bit, little endian, Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
|Memory              |0.62GB/2.02GB
|                    |
|V executable        |/home/admin/v/v
|V last modified time|2025-03-04 09:25:29
|                    |
|V home dir          |OK, value: /home/admin/v
|VMODULES            |OK, value: .vmodules
|VTMP                |OK, value: /tmp/v_0
|Current working dir |OK, value: /home/admin/playground
|                    |
|Git version         |git version 2.39.5
|V git 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
|gcc version         |gcc (Debian 12.2.0-14) 12.2.0
|clang version       |Debian clang version 14.0.6
|tcc version         |tcc version 0.9.28rc 2024-07-31 HEAD@1cee0908 (x86_64 Linux)
|tcc git 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

|emcc version        |N/A
|glibc version       |ldd (Debian GLIBC 2.36-9+deb12u8) 2.36

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[huly-for-github]

Connected to Huly®: V_0.6-22259

[felipensp]

Today you can also pass as argument:

fn t(a struct { name string }) {
	dump(a)
}

t(struct { name: 'Foo'})

[jorgeluismireles]

I see even accept attributes

import json

fn t(a struct { name string @[omitempty] }) {
	println(json.encode(a))
}

t(struct { name: 'Foo'}) // {"name":"Foo"}
t(struct { name: ''})    // {}

This works too:

t(name: 'Foo') // {"name":"Foo"}
t(name: '')    // {}