35 KiB
V Documentation
Introduction
V is a statically typed compiled programming language designed for building maintainable software.
It's similar to Go and is also influenced by Oberon, Rust, Swift.
V is a very simple language. Going through this documentation will take you about half an hour, and by the end of it you will learn pretty much the entire language.
Despite being simple, it gives a lot of power to the developer. Anything you can do in other languages, you can do in V.
Hello World
fn main() {
println('hello world')
}
Functions are declared with fn
. Return type goes after the function
name. In this case main
doesn't return anything, so the type is
omitted.
Just like in C and all related languages, main
is an entry point.
println
is one of the few built-in functions. It prints the value
to standard output.
fn main()
declaration can be skipped in one file programs.
This is useful when writing small programs, "scripts", or just learning
the language. For brevity, fn main()
will be skipped in this
tutorial.
This means that a "hello world" program can be as simple as
println('hello world')
Comments
// This is a single line comment.
/* This is a multiline comment.
/* It can be nested. */
*/
Functions
fn main() {
println(add(77, 33))
println(sub(100, 50))
}
fn add(x int, y int) int {
return x + y
}
fn sub(x, y int) int {
return x - y
}
Again, the type comes after the argument's name.
Just like in Go and C, functions cannot be overloaded. This simplifies the code and improves maintainability and readability.
Functions can be used before their declaration:
add
and sub
are declared after main
, but can still be called from main
.
This is true for all declarations in V and eliminates the need of header files
or thinking about the order of files and declarations.
fn foo() (int, int) {
return 2, 3
}
a, b := foo()
println(a) // 2
println(b) // 3
Functions can return multiple values.
Functions, like consts, and types, are private (not exported) by default.
To allow other modules to use them, prepend pub
. The same applies
to consts and types.
pub fn public_function() {
}
fn private_function() {
}
Variables
name := 'Bob'
age := 20
large_number := i64(9999999999)
println(name)
println(age)
println(large_number)
Variables are declared and initialized with :=
. This is the only
way to declare variables in V. This means that variables always have an initial
value.
The variable's type is inferred from the value on the right hand side.
To force a different type, use type conversion:
the expression T(v)
converts the value v
to the
type T
.
Unlike most other languages, V only allows defining variables in functions. Global (module level) variables are not allowed. There's no global state in V.
mut age := 20
println(age)
age = 21
println(age)
To change the value of the variable use =
. In V, variables are
immutable by default. To be able to change the value of the variable, you have to declare it with mut
.
Try compiling the program above after removing mut
from the first line.
Please note the difference between :=
and =
:=
is used for declaring and initializing, =
is used for assigning.
fn main() {
age = 21
}
This code will not compile, because variable age
is not declared.
All variables need to be declared in V.
fn main() {
age := 21
}
In development mode this code will result in an "unused variable" warning.
In production mode (v -prod foo.v
) it will not compile at all, like in Go.
fn main() {
a := 10
if true {
a := 20
}
}
Unlike most languages, variable shadowing is not allowed. Declaring a variable with a name that is already used in a parent scope will result in a compilation error.
Basic types
bool
string
i8 i16 int i64 i128 (soon)
byte u16 u32 u64 u128 (soon)
rune // represents a Unicode code point
f32 f64
byteptr
voidptr
Please note that unlike C and Go, int
is always a 32 bit integer.
Strings
name := 'Bob'
println('Hello, $name!') // `$` is used for string interpolation
println(name.len)
bobby := name + 'by' // + is used to concatenate strings
println(bobby) // "Bobby"
println(bobby[1..3]) // "ob"
mut s := 'hello '
s += 'world' // `+=` is used to append to a string
println(s) // "hello world"
In V, a string is a read-only array of bytes. String data is encoded using UTF-8.
Strings are immutable.
Both single and double quotes can be used to denote strings. For consistency,
vfmt
converts double quotes to single quotes unless the string contains a single quote character.
Interpolation syntax is pretty simple. It also works with fields:
'age = $user.age'
. If you need more complex expressions, use ${}
: 'can register = ${user.age > 13}'
.
All operators in V must have values of the same type on both sides. This code will not compile if age
is an int
:
println('age = ' + age)
We have to either convert age
to a string
:
println('age = ' + age.str())
or use string interpolation (preferred):
println('age = $age')
To denote character literals, use `
a := `a`
assert 'aloha!'[0] == `a`
For raw strings, prepend r
. Raw strings are not escaped:
s := r'hello\nworld'
println(s) // "hello\nworld"
Arrays
mut nums := [1, 2, 3]
println(nums) // "[1, 2, 3]"
println(nums[1]) // "2"
nums << 4
println(nums) // "[1, 2, 3, 4]"
nums << [5, 6, 7]
println(nums) // "[1, 2, 3, 4, 5, 6, 7]"
mut names := ['John']
names << 'Peter'
names << 'Sam'
// names << 10 <-- This will not compile. `names` is an array of strings.
println(names.len) // "3"
println('Alex' in names) // "false"
names = [] // The array is now empty
// We can also preallocate a certain amount of elements.
ids := [0].repeat(50) // This creates an array with 50 zeros
Array type is determined by the first element: [1, 2, 3]
is an array of ints ([]int
).
['a', 'b']
is an array of strings ([]string
).
All elements must have the same type. [1, 'a']
will not compile.
<<
is an operator that appends a value to the end of the array.
It can also append an entire array.
.len
field returns the length of the array. Note, that it's a read-only field,
and it can't be modified by the user. All exported fields are read-only by default in V.
val in array
returns true if the array contains val
.
All arrays can be easily printed with println(arr)
and converted to a string
with s := arr.str()
.
Arrays can be efficiently filtered and mapped with .filter()
and
.map()
methods:
nums := [1, 2, 3, 4, 5, 6]
even := nums.filter(it % 2 == 0)
println(even) // [2, 4, 6]
words := ['hello', 'world']
upper := words.map(it.to_upper())
println(upper) // ['HELLO', 'WORLD']
it
is a special variable that refers to an element in filter/map methods.
Maps
mut m := map[string]int // Only maps with string keys are allowed for now
m['one'] = 1
m['two'] = 2
println(m['one']) // "1"
println(m['bad_key']) // "0"
println('bad_key' in m) // Use `in` to detect whether such key exists
m.delete('two')
numbers := {
'one': 1,
'two': 2
}
If
a := 10
b := 20
if a < b {
println('$a < $b')
} else if a > b {
println('$a > $b')
} else {
println('$a == $b')
}
if
statements are pretty straightforward and similar to most other languages.
Unlike other C-like languages, there are no parentheses surrounding the condition, and the braces are always required.
if
can be used as an expression:
num := 777
s := if num % 2 == 0 {
'even'
}
else {
'odd'
}
println(s) // "odd"
In operator
in
allows to check whether an array or a map contains an element.
nums := [1, 2, 3]
println(1 in nums) // true
m := {'one': 1, 'two': 2}
println('one' in m) // true
It's also useful for writing more clear and compact boolean expressions:
if parser.token == .plus || parser.token == .minus ||
parser.token == .div || parser.token == .mult {
...
}
if parser.token in [.plus, .minus, .div, .mult] {
...
}
V optimizes such expressions, so both if
statements above produce the same machine code, no arrays are created.
For loop
V has only one looping construct: for
.
numbers := [1, 2, 3, 4, 5]
for num in numbers {
println(num)
}
names := ['Sam', 'Peter']
for i, name in names {
println('$i) $name') // Output: 0) Sam
} // 1) Peter
The for value in
loop is used for going through elements of an array.
If an index is required, an alternative form for index, value in
can be used.
Note, that the value is read-only. If you need to modify the array while looping, you have to use indexing:
mut numbers := [1, 2, 3, 4, 5]
for i, num in numbers {
println(num)
numbers[i] = 0
}
mut sum := 0
mut i := 0
for i <= 100 {
sum += i
i++
}
println(sum) // "5050"
This form of the loop is similar to while
loops in other languages.
The loop will stop iterating once the boolean condition evaluates to false.
Again, there are no parentheses surrounding the condition, and the braces are always required.
mut num := 0
for {
num++
if num >= 10 {
break
}
}
println(num) // "10"
The condition can be omitted, this results in an infinite loop.
for i := 0; i < 10; i++ {
// Don't print 6
if i == 6 {
continue
}
println(i)
}
Finally, there's the traditional C style for
loop. It's safer than the while
form
because with the latter it's easy to forget to update the counter and get
stuck in an infinite loop.
Here i
doesn't need to be declared with mut
since it's always going to be mutable by definition.
Match
os := 'windows'
print('V is running on ')
match os {
'darwin' { println('macOS.') }
'linux' { println('Linux.') }
else { println(os) }
}
number := 2
s := match number {
1 { 'one' }
2 { 'two' }
else { 'many'}
}
A match statement is a shorter way to write a sequence of if - else
statements.
When a matching branch is found, the following statement block will be run, and the final expression will be returned.
The else branch will be evaluated when no other branches match.
enum Color {
red
blue
green
}
fn is_red_or_blue(c Color) bool {
return match c {
.red { true }
.blue { true }
else { false }
}
}
A match statement can also be used to branch on the variants of an enum
by using the shorthand .variant_here
syntax.
Structs
struct Point {
x int
y int
}
p := Point{
x: 10
y: 20
}
println(p.x) // Struct fields are accessed using a dot
Structs are allocated on the stack. To allocate a struct on the heap
and get a reference to it, use the &
prefix:
// Alternative initialization syntax for structs with 3 fields or fewer
p := &Point{10, 10}
// References have the same syntax for accessing fields
println(p.x)
The type of p
is &Point
. It's a reference to Point
.
References are similar to Go pointers and C++ references.
V doesn't have subclassing, but it supports embedded structs:
// TODO: this will be implemented later
struct Button {
Widget
title string
}
button := new_button('Click me')
button.set_pos(x, y)
// Without embedding we'd have to do
button.widget.set_pos(x,y)
Access modifiers
Struct fields are private and immutable by default (making structs immutable as well).
Their access modifiers can be changed with
pub
and mut
. In total, there are 5 possible options:
struct Foo {
a int // private immutable (default)
mut:
b int // private mutable
c int // (you can list multiple fields with the same access modifier)
pub:
d int // public immmutable (readonly)
pub mut:
e int // public, but mutable only in parent module
__global:
f int // public and mutable both inside and outside parent module
} // (not recommended to use, that's why the 'global' keyword
// starts with __)
For example, here's the string
type defined in the builtin
module:
struct string {
str byteptr
pub:
len int
}
It's easy to see from this definition that string
is an immutable type.
The byte pointer with the string data is not accessible outside builtin
at all.
len
field is public, but not mutable:
fn main() {
str := 'hello'
len := str.len // OK
str.len++ // Compilation error
}
Methods
struct User {
age int
}
fn (u User) can_register() bool {
return u.age > 16
}
user := User{age: 10}
println(user.can_register()) // "false"
user2 := User{age: 20}
println(user2.can_register()) // "true"
V doesn't have classes. But you can define methods on types.
A method is a function with a special receiver argument.
The receiver appears in its own argument list between the fn
keyword and the method name.
In this example, the can_register
method has a receiver of type User
named u
.
The convention is not to use receiver names like self
or this
,
but a short, preferably one letter long, name.
Pure functions by default
V functions are pure by default, meaning that their return values are only determined by their arguments, and their evaluation has no side effects.
This is achieved by lack of global variables and all function arguments being immutable by default, even when references are passed.
V is not a pure functional language however.
It is possible to modify function arguments by using the same keyword mut
:
struct User {
mut:
is_registered bool
}
fn (u mut User) register() {
u.is_registered = true
}
mut user := User{}
println(user.is_registered) // "false"
user.register()
println(user.is_registered) // "true"
In this example, the receiver (which is simply the first argument) is marked as mutable,
so register()
can change the user object. The same works with non-receiver arguments:
fn multiply_by_2(arr mut []int) {
for i := 0; i < arr.len; i++ {
arr[i] *= 2
}
}
mut nums := [1, 2, 3]
multiply_by_2(mut nums)
println(nums) // "[2, 4, 6]"
Note, that you have to add mut
before nums
when calling this function. This makes
it clear that the function being called will modify the value.
It is preferable to return values instead of modifying arguments. Modifying arguments should only be done in performance-critical parts of your application to reduce allocations and copying.
For this reason V doesn't allow to modify primitive args like integers, only complex types like arrays and maps.
Use user.register()
or user = register(user)
instead of register(mut user)
.
V makes it easy to return a modified version of an object:
fn register(u User) User {
return { u | is_registered: true }
}
user = register(user)
High order functions
fn sqr(n int) int {
return n * n
}
fn run(value int, op fn(int) int) int {
return op(value)
}
fn main() {
println(run(5, sqr)) // "25"
}
References
fn (foo Foo) bar_method() {
...
}
fn bar_function(foo Foo) {
...
}
If a function argument is immutable like foo
in the examples above,
V can pass it by value or by reference. The decision is made
by the compiler, and the developer doesn't need to think about it.
You no longer need to remember whether you should pass the struct by value or by reference.
There's a way to ensure that the struct is always passed by reference by
adding &
:
fn (foo &Foo) bar() {
println(foo.abc)
}
foo
is still immutable and can't be changed. For that,
(foo mut Foo)
has to be used.
In general, V references are similar to Go pointers and C++ references. For example, a tree structure definition would look like this:
struct Node<T> {
val T
left &Node
right &Node
}
Constants
const (
pi = 3.14
world = '世界'
)
println(pi)
println(world)
Constants are declared with const
. They can only be defined
at the module level (outside of functions).
Constant values can never be changed.
V constants are more flexible than in most languages. You can assign more complex values:
struct Color {
r int
g int
b int
}
fn (c Color) str() string { return '{$c.r, $c.g, $c.b}' }
fn rgb(r, g, b int) Color { return Color{r: r, g: g, b: b} }
const (
numbers = [1, 2, 3]
red = Color{r: 255, g: 0, b: 0}
blue = rgb(0, 0, 255)
)
println(numbers)
println(red)
println(blue)
Global variables are not allowed, so this can be really useful.
When naming constants, snake_case must be used.
Many people prefer all caps consts: TOP_CITIES
. This wouldn't work
well in V, because consts are a lot more powerful than in other languages.
They can represent complex structures, and this is used quite often since there
are no globals:
println('Top cities: $TOP_CITIES.filter(.usa)')
vs
println('Top cities: $top_cities.filter(.usa)')
println
println
is a simple yet powerful builtin function. It can print anything:
strings, numbers, arrays, maps, structs.
println(1) // "1"
println('hi') // "hi"
println([1,2,3]) // "[1, 2, 3]"
println(User{name:'Bob', age:20}) // "User{name:'Bob', age:20}"
If you want to define a custom print value for your type, simply define a
.str() string
method.
If you don't want to print a newline, use print()
instead.
Modules
V is a very modular language. Creating reusable modules is encouraged and is very simple. To create a new module, create a directory with your module's name and .v files with code:
cd ~/code/modules
mkdir mymodule
vim mymodule/mymodule.v
// mymodule.v
module mymodule
// To export a function we have to use `pub`
pub fn say_hi() {
println('hello from mymodule!')
}
You can have as many .v files in mymodule/
as you want.
Build it with v build module ~/code/modules/mymodule
.
That's it, you can now use it in your code:
module main
import mymodule
fn main() {
mymodule.say_hi()
}
Note that you have to specify the module every time you call an external function. This may seem verbose at first, but it makes code much more readable and easier to understand, since it's always clear which function from which module is being called. Especially in large code bases.
Module names should be short, under 10 characters. Circular imports are not allowed.
You can create modules anywhere.
All modules are compiled statically into a single executable.
If you want to write a module that will automatically call some
setup/initialization code when imported (perhaps you want to call
some C library functions), write a module init
function inside the module:
fn init() int {
// your setup code here ...
return 1
}
The init function cannot be public. It will be called automatically.
Interfaces
struct Dog {}
struct Cat {}
fn (d Dog) speak() string {
return 'woof'
}
fn (c Cat) speak() string {
return 'meow'
}
interface Speaker {
speak() string
}
fn perform(s Speaker) string {
return s.speak()
}
dog := Dog{}
cat := Cat{}
println(perform(dog)) // "woof"
println(perform(cat)) // "meow"
A type implements an interface by implementing its methods. There is no explicit declaration of intent, no "implements" keyword.
Enums
enum Color {
red green blue
}
mut color := Color.red
// V knows that `color` is a `Color`. No need to use `color = Color.green` here.
color = .green
println(color) // "1" TODO: print "green"?
Option/Result types & error handling
struct User {
id int
name string
}
struct Repo {
users []User
}
fn new_repo() Repo {
return Repo {
users: [User{1, 'Andrew'}, User {2, 'Bob'}, User {10, 'Charles'}]
}
}
fn (r Repo) find_user_by_id(id int) ?User {
for user in r.users {
if user.id == id {
// V automatically wraps this into an option type
return user
}
}
return error('User $id not found')
}
fn main() {
repo := new_repo()
user := repo.find_user_by_id(10) or { // Option types must be handled by `or` blocks
return // `or` block must end with `return`, `break`, or `continue`
}
println(user.id) // "10"
println(user.name) // "Charles"
}
V combines Option
and Result
into one type, so you don't need to decide which one to use.
The amount of work required to "upgrade" a function to an optional function is minimal:
you have to add a ?
to the return type and return an error when something goes wrong.
If you don't need to return an error, you can simply return none
.
This is the primary way of handling errors in V. They are still values, like in Go, but the advantage is that errors can't be unhandled, and handling them is a lot less verbose.
err
is defined inside an or
block and is set to the string message passed
to the error()
function. err
is empty if none
was returned.
user := repo.find_user_by_id(7) or {
println(err) // "User 7 not found"
return
}
You can also propagate errors:
resp := http.get(url)?
println(resp.body)
http.get
returns ?http.Response
. It was called with ?
, so the error is propagated to the calling function
(which must return an optional) or in case of main
leads to a panic.
Basically the code above is a shorter version of
resp := http.get(url) or {
panic(err)
}
println(resp.body)
V does not have a way to force unwrap an optional (like Rust's unwrap()
or Swift's !
). You have to use or { panic(err) }
instead.
Generics
struct Repo<T> {
db DB
}
fn new_repo<T>(db DB) Repo<T> {
return Repo<T>{db: db}
}
// This is a generic function. V will generate it for every type it's used with.
fn (r Repo<T>) find_by_id(id int) ?T {
table_name := T.name // in this example getting the name of the type gives us the table name
return r.db.query_one<T>('select * from $table_name where id = ?', id)
}
db := new_db()
users_repo := new_repo<User>(db)
posts_repo := new_repo<Post>(db)
user := users_repo.find_by_id(1)?
post := posts_repo.find_by_id(1)?
Concurrency
The concurrency model is very similar to Go. To run foo()
concurrently, just
call it with go foo()
. Right now, it launches the function in a new system
thread. Soon coroutines and the scheduler will be implemented.
Decoding JSON
import json
struct User {
name string
age int
// Use the `skip` attribute to skip certain fields
foo Foo [skip]
// If the field name is different in JSON, it can be specified
last_name string [json:lastName]
}
data := '{ "name": "Frodo", "lastName": "Baggins", "age": 25 }'
user := json.decode(User, data) or {
eprintln('Failed to decode json')
return
}
println(user.name)
println(user.last_name)
println(user.age)
JSON is very popular nowadays, that's why JSON support is built in.
The first argument of the json.decode
function is the type to decode to.
The second argument is the JSON string.
V generates code for JSON encoding and decoding. No runtime reflection is used. This results in much better performance.
Testing
// hello.v
fn hello() string {
return 'Hello world'
}
// hello_test.v
fn test_hello() {
assert hello() == 'Hello world'
}
All test functions have to be placed in *_test.v
files and begin with test_
.
To run the tests do v hello_test.v
. To test an entire module, do
v test mymodule
.
assert
keyword can be used outside of tests as well.
Memory management
(Work in progress) There's no garbage collection or reference counting. V cleans everything up during compilation. If your V program compiles, it's guaranteed that it's going to be leak free. For example:
fn draw_text(s string, x, y int) {
...
}
fn draw_scene() {
...
draw_text('hello $name1', 10, 10)
draw_text('hello $name2', 100, 10)
draw_text(strings.repeat('X', 10000), 10, 50)
...
}
The strings don't escape draw_text
, so they are cleaned up when
the function exits.
In fact, the first two calls won't result in any allocations at all. These two strings are small, V will use a preallocated buffer for them.
fn test() []int {
number := 7 // stack variable
user := User{} // struct allocated on stack
numbers := [1, 2, 3] // array allocated on heap, will be freed as the function exits
println(number)
println(user)
println(numbers)
numbers2 := [4, 5, 6] // array that's being returned, won't be freed here
return numbers2
}
Defer
A defer statement defers the execution of a block of statements until the surrounding function returns.
fn read_log() {
f := os.open('log.txt')
defer { f.close() }
...
if !ok {
// defer statement will be called here, the file will be closed
return
}
...
// defer statement will be called here, the file will be closed
}
ORM
(alpha)
V has a built-in ORM that supports Postgres, and will soon support MySQL and SQLite.
The benefits of V ORM:
- One syntax for all SQL dialects. Migrating to a different database becomes much easier.
- Queries are constructed with V syntax. There's no need to learn another syntax.
- Safety. It's impossible to construct a SQL query with an injection.
- Compile time checks. No more typos that can only be caught at runtime.
- Readability and simplicity. You don't need to manually parse the results and construct objects.
struct Customer { // struct name has to be the same as the table name for now
id int // an integer id must be the first field
name string
nr_orders int
country string
}
db := pg.connect(db_name, db_user)
// select count(*) from Customer
nr_customers := db.select count from Customer
println('number of all customers: $nr_customers')
// V syntax can be used to build queries
// db.select returns an array
uk_customers := db.select from Customer where country == 'uk' && nr_orders > 0
println(uk_customers.len)
for customer in uk_customers {
println('$customer.id - $customer.name')
}
// by adding `limit 1` we tell V that there will be only one object
customer := db.select from Customer where id == 1 limit 1
println('$customer.id - $customer.name')
// insert a new customer
new_customer := Customer{name: 'Bob', nr_orders: 10}
db.insert(new_customer)
vfmt
You don't need to worry about formatting your code or style guidelines. vfmt takes care of that:
v fmt file.v
It's recommended to set up your editor, so that vfmt runs on every save.
Always run vfmt before pushing your code.
writing_documentation
The way it works is very similar to Go. It's very simple: there's no need to write documentation for your code, vdoc will generate it from the source code.
Documentation for each function/type/const must be placed right before the declaration:
// clearall clears all bits in the array
fn clearall() {
}
The comment must start with the name of the definition.
An overview of the module must be placed in the first comment right after the module's name.
To generate documentation, run v doc path/to/module
(TODO this is
temporarily disabled).
Advanced Topics
Calling C functions from V
#flag -lsqlite3
#include "sqlite3.h"
struct C.sqlite3
struct C.sqlite3_stmt
fn C.sqlite3_column_int(stmt C.sqlite3_stmt, n int) int
fn main() {
path := 'users.db'
db := &C.sqlite3{!} // a temporary hack meaning `sqlite3* db = 0`
C.sqlite3_open(path.str, &db)
query := 'select count(*) from users'
stmt := &C.sqlite3_stmt{!}
C.sqlite3_prepare_v2(db, query.str, - 1, &stmt, 0)
C.sqlite3_step(stmt)
nr_users := C.sqlite3_column_int(stmt, 0)
C.sqlite3_finalize(stmt)
println(nr_users)
}
Add #flag
directives to the top of your V files to provide C compilation flags like -l
for
linking, -I
for adding include files locations, -D
for setting compile time variables, etc.
You can use different flags for different targets. Right now, linux
, darwin
, and windows
are supported.
For now you have to use one flag per line:
#flag linux -lsdl2
#flag linux -Ivig
#flag linux -DCIMGUI_DEFINE_ENUMS_AND_STRUCTS=1
#flag linux -DIMGUI_DISABLE_OBSOLETE_FUNCTIONS=1
#flag linux -DIMGUI_IMPL_API=
C strings can be converted to V strings with string(cstring)
or string(cstring, len)
.
V uses voidptr
for C's void*
and byteptr
for C's byte*
or char*
.
To cast voidptr
to V references use user := &User(user_void_ptr)
.
voidptr
can also be dereferenced to V structs by casting: user := User(user_void_ptr)
.
Check out socket.v for an example of calling C code from V: https://github.com/vlang/v/blob/master/vlib/net/socket.v
To debug issues with the C code, v -show_c_cmd .
is useful. It prints the
C command that is used to build the program.
Compile time if
$if windows {
println('Windows')
}
$if linux {
println('Linux')
}
$if macos {
println('macOS')
}
$if debug {
println('debugging')
}
Compile time if
starts with a $
. Right now it can only be used to detect
an OS or a -debug
compilation option.
Reflection via codegen
Having built-in JSON support is nice, but V also allows you to create efficient serializers for anything:
// TODO: not implemented yet
fn decode<T>(data string) T {
mut result := T{}
for field in T.fields {
if field.typ == 'string' {
result.$field = get_string(data, field.name)
} else if field.typ == 'int' {
result.$field = get_int(data, field.name)
}
}
return result
}
// generates to:
fn decode_User(data string) User {
mut result := User{}
result.name = get_string(data, 'name')
result.age = get_int(data, 'age')
return result
}
Limited operator overloading
struct Vec {
x int
y int
}
fn (a Vec) str() string {
return '{$a.x, $a.y}'
}
fn (a Vec) + (b Vec) Vec {
return Vec {
a.x + b.x,
a.y + b.y
}
}
fn (a Vec) - (b Vec) Vec {
return Vec {
a.x - b.x,
a.y - b.y
}
}
fn main() {
a := Vec{2, 3}
b := Vec{4, 5}
println(a + b) // "{6, 8}"
println(a - b) // "{-2, -2}"
}
Operator overloading goes against V's philosophy of simplicity and predictability. But since scientific and graphical applications are among V's domains, operator overloading is very important to have in order to improve readability:
a.add(b).add(c.mul(d))
is a lot less readable than a + b + c * d
.
To improve safety and maintainability, operator overloading has several limitations:
-It's only possible to overload +, -, *, /
operators.
-
Calling other functions inside operator functions is not allowed.
-
Operator functions can't modify their arguments.
-
Both arguments must have the same type (just like with all operators in V).
Inline assembly
TODO: not implemented yet
fn main() {
a := 10
asm x64 {
mov eax, [a]
add eax, 10
mov [a], eax
}
}
Translating C/C++ to V
TODO: translating C to V will be available in V 0.3. C++ to V will be available later this year.
V can translate your C/C++ code to human readable V code.
Let's create a simple program test.cpp
first:
#include <vector>
#include <string>
#include <iostream>
int main() {
std::vector<std::string> s;
s.push_back("V is ");
s.push_back("awesome");
std::cout << s.size() << std::endl;
return 0;
}
Run v translate test.cpp
and V will generate test.v
:
fn main {
mut s := []
s << 'V is '
s << 'awesome'
println(s.len)
}
An online C/C++ to V translator is coming soon.
When should you translate C code and when should you simply call C code from V?
If you have well-written, well-tested C code, then of course you can always simply call this C code from V.
Translating it to V gives you several advantages:
-
If you plan to develop that code base, you now have everything in one language, which is much safer and easier to develop in than C.
-
Cross-compilation becomes a lot easier. You don't have to worry about it at all.
-
No more build flags and include files either.
Hot code reloading
module main
import time
import os
[live]
fn print_message() {
println('Hello! Modify this message while the program is running.')
}
fn main() {
for {
print_message()
time.sleep_ms(500)
}
}
Build this example with v -live message.v
.
Functions that you want to be reloaded must have [live]
attribute
before their definition.
Right now it's not possible to modify types while the program is running.
More examples, including a graphical application: github.com/vlang/v/tree/master/examples/hot_code_reloading.
Cross compilation
To cross compile your project simply run
v -os windows .
or
v -os linux .
(Cross compiling for macOS is temporarily not possible.)
If you don't have any C dependencies, that's all you need to do. This works even
when compiling GUI apps using the ui
module or graphical apps using gg
.
You will need to install Clang, LLD linker, and download a zip file with libraries and include files for Windows and Linux. V will provide you with a link.
Cross-platform shell scripts in V
V can be used as an alternative to Bash to write deployment scripts, build scripts, etc.
The advantage of using V for this is the simplicity and predictability of the language, and cross-platform support. "V scripts" run on Unix-like systems as well as on Windows.
Use .vsh file extension. It will make all functions in the os
module global (so that you can use ls()
instead of os.ls()
, for example).
rm('build/*')
// Same as:
for file in ls('build/') {
rm(file)
}
mv('*.v', 'build/')
// Same as:
for file in ls('.') {
if file.ends_with('.v') {
mv(file, 'build/')
}
}
Now you can either compile this like a normal V program and get an executable you can deploy and run
anywhere:
v deploy.v && ./deploy
Or just run it more like a traditional bash script:
v run deploy.v
Appendix I: Keywords
V has 23 keywords:
break
const
continue
defer
else
enum
fn
for
go
goto
if
import
in
interface
match
module
mut
none
or
pub
return
struct
type
Appendix II: Operators
+ sum integers, floats, strings
- difference integers, floats
* product integers, floats
/ quotient integers, floats
% remainder integers
& bitwise AND integers
| bitwise OR integers
^ bitwise XOR integers
<< left shift integer << unsigned integer
>> right shift integer >> unsigned integer
Precedence Operator
5 * / % << >> &
4 + - | ^
3 == != < <= > >=
2 &&
1 ||
Assignment Operators
+= -= *= /= %=
&= |= ^=
>>= <<=