Tuple types in zig

tuple.zig

const std = @import("std");
const TypeId = @import("builtin").TypeId;
const allocPrint = std.fmt.allocPrint;

// This should be equivalent to Tuple(f32, f32)
fn TestTuple() type {
    return struct {
        const Self = this;
        const Types = []type { f32, f32 };

        field0: f32,
        field1: f32,

        fn init(arg0: f32, arg1: f32) Self {
            return Self {
                .field0 = arg0,
                .field1 = arg1
            };
        }

        fn get(self: &Self, comptime i: usize) &(@memberType(Self, i)) {
            return if (i == 0) &self.field0 else &self.field1;
        }

        // Takes a series of pointers or nullable pointers and unpacks the tuple fields into them.
        // null pointers are ignored.
        fn unpack(self: &const Self, args: ...) void {
            if (args.len == 0) {
                @compileError("You have to unpack at least one field.");
            }

            if (args.len > Self.Types.len) {
                @compileError("Cannot unpack more fields than the tuple has.");
            }

            comptime var i = 0;
            inline while (i < args.len) : (i += 1) {
                comptime var nullable = false;

                if (@typeId(@typeOf(args[i])) == TypeId.Nullable) {
                    nullable = true;
                }

                comptime const arg_type = if (nullable) @typeOf(args[i]).Child else @typeOf(args[i]);
                comptime const type_id = @typeId(arg_type);

                if (type_id != TypeId.Pointer) {
                    @compileError("Must pass pointers to unpack.");
                }

                if (arg_type.Child != Self.Types[i]) {
                    @compileError("Invalid pointer type.");
                }

                if (nullable) {
                    if (args[i] != null) {
                        *??args[i] = if (i == 0) self.field0 else self.field1;
                    }
                } else {
                    *args[i] = if (i == 0) self.field0 else self.field1;
                }
            }
        }
    };
}

fn ChildRefType(comptime ref_type: type, comptime i: usize) type {
    // TODO: Check for constness of ref_type, propagate it to the result type
    return &(@memberType(ref_type.Child, i));
}

// get the i'th field of a struct
pub fn get(self: var, comptime i: usize) ChildRefType(@typeOf(self), i) {
    return if (i == 0) &self.field0 else &self.field1;
}

pub fn Tuple(comptime types: []type) type {
    if (types.len == 0) {
        @compileError("No types passed to Tuple.");
    }

    var allocator_data: [1024 * 8]u8 = undefined;
    const alloc = &std.heap.FixedBufferAllocator.init(allocator_data).allocator;

    var member_names: [types.len][]const u8 = undefined;
    var member_types: [types.len][]const &TypeInfo = undefined;

    for (types) |t, i| {
        member_names[i] = allocPrint(alloc, "field{}", i) catch unreachable;
        member_types[i] = @reflect(t);
    }

    // Free the member names upon exiting the function.
    defer for (member_names) |m| {
        alloc.free(m);
    };

    // Build our tuple type.
    // These types should be builtin so no need for import, right?
    const struct_detail = StructTypeInfoDetail.init(false, member_names, member_types);

    const detail = TypeInfoDetail {
        .Struct = struct_detail
    };

    // Perhaps:
    // const detail = TypeInfoDetail.init(TypeId.Struct, false, member_names, member_types);

    // TODO: Add methods
    // init(args: ...), get(comptime i: usize) &types[i], ...
    const type_info = TypeInfo.init(false, false, detail);

    return @reify(type_info);

    // TODO: Better TypeBuilder interface, look at the TypeId's currently available.
    // var builder = TypeBuilder.init();
    // builder.buildTypeAndStuff();
    // @reify(builder)
}

fn vararg_types(args: ...) []type {
    var ts: [args.len]type = undefined;
    
    var i = 0;
    while (i < args.len) : (i += 1) {
        ts[i] = @typeOf(args[i]);
    }

    return ts;
}

pub fn make_tuple(args: ...) Tuple(vararg_types(args)) {
    const TupleType = @typeOf(this).ReturnType;

    var tup: TupleType = undefined;
    inline for (args) |arg, i| {
        *tup.get(i) = arg;
    }

    return tup;
}

pub fn main() !void {
    var stdout_file = try std.io.getStdOut();
    var adapter = std.io.FileOutStream.init(&stdout_file);
    var stream = &adapter.stream;

    const Point = TestTuple();
    //const Point = Tuple(f32, f32);

    var p = Point.init(0.0, 0.0);
    try stream.print("({}, {})\n", *p.get(0), *p.get(1));

    *p.get(0) = 1.0;

    try stream.print("({}, {})\n", *p.get(0), *p.get(1));

    *get(p, 1) = 1.0;

    try stream.print("({}, {})\n", *p.get(0), *p.get(1));

    *p.get(1) = 2.0;

    var to_unpack: f32 = undefined;
    var nullable: ?&f32 = null;
    p.unpack(nullable, &to_unpack);

    try stream.print("UNPACKED {}\n", to_unpack);

    // const pp = Point.init(1.0, 1.0);
    // *get(pp, 0) = 2.0;
}