24: Mixins - royal-lang/rl GitHub Wiki

Mixins can be used to mix-in a piece of code directly at compile-time either using a string or a template.

Mixins are alternatives to manipulating the AST directly. AST manipulation can be done during compile-time with CTFE.

Prior to a mixin statement the module of the mixin statement must be syntactic valid which means you cannot use mixins to create obscure syntaxes etc.

mixin(MIXIN_STRING);
mixin(MIXIN_TEMPLATE);

mixin template NAME(TEMPLATE_PARAMS)
{
    CODE_TO_MIXIN
}

Example:

fn main()
{
    mixin("var x = 10;");
    mixin("var y = x * 10;");
    mixin("var result = x + y");

    mixin("writeln(result);");
}

Result:

fn main()
{
    var x = 10;
    var y = x * 10;
    var result = x + y;

    writeln(result);
}

---

mixin template Header
{
    uint size;
    uint id;
}

struct DataPacket
{
    mixin(Header);

    ushort magic;
}

var DataPacket packet;
packet.size = 10;
packet.id = 2002;
packet.magic = 3;