doc: update condif section (#6418)

pull/6424/head^2
Lukas Neubert 2020-09-18 23:48:59 +02:00 committed by GitHub
parent 3126ae305c
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1 changed files with 46 additions and 16 deletions

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@ -2251,26 +2251,56 @@ To see a detailed list of all flags that V supports, use `v help`, `v help build
## Conditional compilation
```v
$if windows {
println('Windows')
// Support for multiple conditions in one branch
$if ios || android {
println('Running on a mobile device!')
}
$if linux {
println('Linux')
}
$if macos {
println('macOS')
}
$else {
println('different OS')
$if linux && x64 {
println('64-bit Linux.')
}
// Usage as expression
os := $if windows { 'Windows' } $else { 'UNIX' }
println('Using $os')
// $else-$if branches
$if tinyc {
println('tinyc')
} $else $if clang {
println('clang')
} $else $if gcc {
println('gcc')
} $else {
println('different compiler')
}
$if test {
println('testing')
}
// v -cg ...
$if debug {
println('debugging')
}
// v -d option ...
$if option ? {
println('custom option')
}
```
If you want an `if` to be evaluated at compile time it must be prefixed with a `$` sign. Right now it can only be used to detect
an OS or a `-debug` compilation option.
If you want an `if` to be evaluated at compile time it must be prefixed with a `$` sign.
Right now it can be used to detect an OS, compiler, platform or compilation options.
`$if debug` is a special option like `$if windows` or `$if x32`.
If you're using a custom ifdef, then you do need `$if option ? {}` and compile with`v -d option`.
Full list of builtin options:
| OS | Compilers | Platforms | Other |
| --- | --- | --- | --- |
| `windows`, `linux`, `macos` | `gcc`, `tinyc` | `amd64`, `aarch64` | `debug`, `test`, `js` |
| `mac`, `darwin`, `ios`, | `clang`, `mingw` | `x64`, `x32` | `glibc`, `prealloc` |
| `android`,`mach`, `dragonfly` | `msvc` | `little_endian` | `no_bounds_checking` |
| `gnu`, `hpux`, `haiku`, `qnx` | `cplusplus` | `big_endian` | |
| `solaris`, `linux_or_macos` | | | |
## Compile time pseudo variables
@ -2336,7 +2366,7 @@ Having built-in JSON support is nice, but V also allows you to create efficient
serializers for any data format. V has compile-time `if` and `for` constructs:
```v
// TODO: not implemented yet
// TODO: not fully implemented
struct User {
name string
@ -2352,7 +2382,7 @@ fn decode<T>(data string) T {
$if field.Type is string {
// $(string_expr) produces an identifier
result.$(field.name) = get_string(data, field.name)
} else $if field.Type is int {
} $else $if field.Type is int {
result.$(field.name) = get_int(data, field.name)
}
}