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doc: improve types order (#16399)

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@ -113,11 +113,11 @@ To do so, run the command `v up`.
<tr><td width=33% valign=top> <tr><td width=33% valign=top>
* [Type Declarations](#type-declarations) * [Type Declarations](#type-declarations)
* [Interfaces](#interfaces)
* [Function Types](#function-types)
* [Enums](#enums)
* [Sum types](#sum-types)
* [Type aliases](#type-aliases) * [Type aliases](#type-aliases)
* [Enums](#enums)
* [Function Types](#function-types)
* [Interfaces](#interfaces)
* [Sum types](#sum-types)
* [Option/Result types & error handling](#optionresult-types-and-error-handling) * [Option/Result types & error handling](#optionresult-types-and-error-handling)
* [Handling optionals/results](#handling-optionalsresults) * [Handling optionals/results](#handling-optionalsresults)
* [Custom error types](#custom-error-types) * [Custom error types](#custom-error-types)
@ -2966,7 +2966,185 @@ particularly useful for initializing a C library.
## Type Declarations ## Type Declarations
### Type aliases
To define a new type `NewType` as an alias for `ExistingType`,
do `type NewType = ExistingType`.<br/>
This is a special case of a [sum type](#sum-types) declaration.
### Enums
```v
enum Color as u8 {
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) // "green"
match color {
.red { println('the color was red') }
.green { println('the color was green') }
.blue { println('the color was blue') }
}
```
The enum type can be any integer type, but can be ommited, if it is `int`: `enum Color {`.
Enum match must be exhaustive or have an `else` branch.
This ensures that if a new enum field is added, it's handled everywhere in the code.
Enum fields cannot re-use reserved keywords. However, reserved keywords may be escaped
with an @.
```v
enum Color {
@none
red
green
blue
}
color := Color.@none
println(color)
```
Integers may be assigned to enum fields.
```v
enum Grocery {
apple
orange = 5
pear
}
g1 := int(Grocery.apple)
g2 := int(Grocery.orange)
g3 := int(Grocery.pear)
println('Grocery IDs: $g1, $g2, $g3')
```
Output: `Grocery IDs: 0, 5, 6`.
Operations are not allowed on enum variables; they must be explicitly cast to `int`.
Enums can have methods, just like structs.
```v
enum Cycle {
one
two
three
}
fn (c Cycle) next() Cycle {
match c {
.one {
return .two
}
.two {
return .three
}
.three {
return .one
}
}
}
mut c := Cycle.one
for _ in 0 .. 10 {
println(c)
c = c.next()
}
```
Output:
```
one
two
three
one
two
three
one
two
three
one
```
### Function Types
You can use type aliases for naming specific function signatures - for
example:
```v
type Filter = fn (string) string
```
This works like any other type - for example, a function can accept an
argument of a function type:
```v
type Filter = fn (string) string
fn filter(s string, f Filter) string {
return f(s)
}
```
V has duck-typing, so functions don't need to declare compatibility with
a function type - they just have to be compatible:
```v
fn uppercase(s string) string {
return s.to_upper()
}
// now `uppercase` can be used everywhere where Filter is expected
```
Compatible functions can also be explicitly cast to a function type:
```v oksyntax
my_filter := Filter(uppercase)
```
The cast here is purely informational - again, duck-typing means that the
resulting type is the same without an explicit cast:
```v oksyntax
my_filter := uppercase
```
You can pass the assigned function as an argument:
```v oksyntax
println(filter('Hello world', my_filter)) // prints `HELLO WORLD`
```
And you could of course have passed it directly as well, without using a
local variable:
```v oksyntax
println(filter('Hello world', uppercase))
```
And this works with anonymous functions as well:
```v oksyntax
println(filter('Hello world', fn (s string) string {
return s.to_upper()
}))
```
You can see the complete
[example here](https://github.com/vlang/v/tree/master/examples/function_types.v).
### Interfaces ### Interfaces
```v ```v
// interface-example.1 // interface-example.1
struct Dog { struct Dog {
@ -3198,177 +3376,6 @@ pub interface ReaderWriter {
} }
``` ```
### Function Types
You can use type aliases for naming specific function signatures - for
example:
```v
type Filter = fn (string) string
```
This works like any other type - for example, a function can accept an
argument of a function type:
```v
type Filter = fn (string) string
fn filter(s string, f Filter) string {
return f(s)
}
```
V has duck-typing, so functions don't need to declare compatibility with
a function type - they just have to be compatible:
```v
fn uppercase(s string) string {
return s.to_upper()
}
// now `uppercase` can be used everywhere where Filter is expected
```
Compatible functions can also be explicitly cast to a function type:
```v oksyntax
my_filter := Filter(uppercase)
```
The cast here is purely informational - again, duck-typing means that the
resulting type is the same without an explicit cast:
```v oksyntax
my_filter := uppercase
```
You can pass the assigned function as an argument:
```v oksyntax
println(filter('Hello world', my_filter)) // prints `HELLO WORLD`
```
And you could of course have passed it directly as well, without using a
local variable:
```v oksyntax
println(filter('Hello world', uppercase))
```
And this works with anonymous functions as well:
```v oksyntax
println(filter('Hello world', fn (s string) string {
return s.to_upper()
}))
```
You can see the complete
[example here](https://github.com/vlang/v/tree/master/examples/function_types.v).
### Enums
```v
enum Color as u8 {
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) // "green"
match color {
.red { println('the color was red') }
.green { println('the color was green') }
.blue { println('the color was blue') }
}
```
The enum type can be any integer type, but can be ommited, if it is `int`: `enum Color {`.
Enum match must be exhaustive or have an `else` branch.
This ensures that if a new enum field is added, it's handled everywhere in the code.
Enum fields cannot re-use reserved keywords. However, reserved keywords may be escaped
with an @.
```v
enum Color {
@none
red
green
blue
}
color := Color.@none
println(color)
```
Integers may be assigned to enum fields.
```v
enum Grocery {
apple
orange = 5
pear
}
g1 := int(Grocery.apple)
g2 := int(Grocery.orange)
g3 := int(Grocery.pear)
println('Grocery IDs: $g1, $g2, $g3')
```
Output: `Grocery IDs: 0, 5, 6`.
Operations are not allowed on enum variables; they must be explicitly cast to `int`.
Enums can have methods, just like structs.
```v
enum Cycle {
one
two
three
}
fn (c Cycle) next() Cycle {
match c {
.one {
return .two
}
.two {
return .three
}
.three {
return .one
}
}
}
mut c := Cycle.one
for _ in 0 .. 10 {
println(c)
c = c.next()
}
```
Output:
```
one
two
three
one
two
three
one
two
three
one
```
### Sum types ### Sum types
A sum type instance can hold a value of several different types. Use the `type` A sum type instance can hold a value of several different types. Use the `type`
@ -3533,12 +3540,6 @@ fn pass_time(w World) {
} }
``` ```
### Type aliases
To define a new type `NewType` as an alias for `ExistingType`,
do `type NewType = ExistingType`.<br/>
This is a special case of a [sum type](#sum-types) declaration.
### Option/Result types and error handling ### Option/Result types and error handling
Optional types are for types which may represent `none`. Result types may Optional types are for types which may represent `none`. Result types may