Compile-Time Context

Four values describe the build a program is part of. The compiler fills them in before compiling starts, and Core declares them, so each is imported by its # name:

import Core::{ #target, #build, #compiler, #source };

A fifth, #config, carries values the build is given — see Config. The struct and enum types (Target, OperatingSystem, BuildMode, …) are ordinary Core declarations; import them too when code names them, as in OperatingSystem::Linux or BuildMode::Debug.

Fields are read with ., are lowerCamelCase, and are fixed for the whole build. A read can drive a when, initialize a scalar constant, or appear in any expression, where it compiles to a constant. Text fields (char8[..]) work in expressions and conditions; a const of slice type, though, must be initialized with a literal, so const Date: char8[..] = #build.date; is refused with a constant sequence must be initialized with an array literal or a string literal — use a let instead.

#target

The machine the program will run on — not the machine compiling it. rux build --target linux-x86_64 on Windows answers every field for Linux.

The eight supported targets:

HasFeature takes a TargetFeature. A build for the machine running the compiler reports the features that compiler was itself built to use; a build for any other target reports none. Inside a when condition the shorthand .AVX2 works; in an ordinary expression write TargetFeature::AVX2. An unknown name is an error (unknown target feature '.MMX').

import Core::{ #target };

when #target.arch == .X86_64 && #target.HasFeature(.AVX2) {
    func Kernel() -> char8[..] { return "avx2"; }
} else {
    func Kernel() -> char8[..] { return "scalar"; }
}

#build

The build profile and what it produces. Every field is the same everywhere in one build.

profile is a name, and a project may define profiles of its own; branch on mode, which every profile has. debugAssertions decides whether DebugAssert is kept — when it is false the call is removed and its arguments are not evaluated. The timestamp is taken once per build, and honours the SOURCE_DATE_EPOCH environment variable for reproducible builds.

import Core::{ #build, BuildMode };
import Io::PrintLine;

func Main() -> int {
    when #build.mode == BuildMode::Debug {
        PrintLine("debug build of {} at {}", #build.date, #build.time);
    }
    return 0;
}

#compiler

SemanticVersion is an ordinary struct with the comparison operators == != < <= > >= and the methods Compare, IsEqualTo, IsLessThan, IsAtMost, IsGreaterThan and IsAtLeast, all of which work in a when. A version to compare against is a struct literal constant — a constructor call is a run-time call and is refused (call to 'SemanticVersion' is not a compile-time value):

import Core::{ #compiler, SemanticVersion };

const Rux040 = SemanticVersion { major: 0, minor: 4, patch: 0 };

when #compiler.version.IsAtLeast(Rux040) {
    const HasDefines: bool = true;
} else {
    const HasDefines: bool = false;
}

HasFeature is the better test when code needs one capability rather than a release: it names what is needed and stays right however releases are numbered. Its argument must be a string literal; an unknown name is simply false. Rux 0.4.0 reports:

#source

Each read of #source describes the place where that read is written — the expression itself, not the function around it or its caller.

A helper that reads #source in its own body always reports its own body. To report where it was called from, the caller reads #source and passes the value:

import Core::{ #source };
import Io::PrintLine;

func LogAt(line: uint, message: char8[..]) {
    PrintLine("line {}: {}", line, message);
}

func Main() -> int {
    LogAt(#source.line, "first call");    // the line of this call
    LogAt(#source.line, "second call");   // and of this one
    return 0;
}

The same rule covers a default argument. func LogAt(message: char8[..], line: uint = #source.line) reports the line where the default is written — the parameter list — for every call, so a default does not capture the caller's location. Pass the location explicitly, as above.

Enum reference

Every enum here is a Core declaration with a uint8 representation.

No supported build produces an Unknown variant; it exists so a provider can describe a target the compiler has no name for. The variant is .macOS, with a lower-case m.

See also

• Conditional compilation — branching on these values
• Config — #config, the build's own values
• Intrinsics — how Core declares them
• API: Target, Build, Compiler, Source
• Learn: Target, Build mode, Source location