concatenating arrays at compile-time

concatarr.zig

const std = @import("std");
const warn = std.debug.warn;

pub fn main() void {
    comptime var x1 = []f64{1, 2, 3};
    comptime var x2 = x1 ++ x1;  // error to assign x1 here

    comptime var x3 = ([]f64{1, 2, 3})[0..];
    x3 = x3 ++ x3; // no error

    warn("x2: {}\n", @typeName(@typeOf(x2)));
    warn("x3: {}\n", @typeName(@typeOf(x3)));
}