goto-less.zig

pub fn exprNumListToBytes(mem: *std.mem.Allocator, maybeNumList: ?[]const Expr) !?[]const u8 {
    if (maybeNumList) |it| {
        const bytes = try mem.alloc(u8, it.len);
        for (it) |expr, i|
            if (expr.is(.NumInt)) |n| { // .is() expands to: switch(expr) { .NumInt => |n| ..., else => ... }
                if (n >= 0 and n <= 255)
                    bytes[i] = @intCast(u8, n)
                else {
                    mem.free(bytes);
                    return null;
                }
            } else {
                mem.free(bytes);
                return null;
            };
        return bytes;
    }
    return null;
}

With goto could do instead:

pub fn exprNumListToBytes(mem: *std.mem.Allocator, maybeNumList: ?[]const Expr) !?[]const u8 {
    if (maybeNumList) |it| {
        const bytes = try mem.alloc(u8, it.len);
        for (it) |expr, i|
            if (expr.is(.NumInt)) |n| { // .is() expands to: switch(expr) { .NumInt => |n| ..., else => ... }
                if (n >= 0 and n <= 255)
                    bytes[i] = @intCast(u8, n)
                else
                    goto nope;
            } else
                goto nope;
        return bytes;
        nope:
            mem.free(bytes);
    }
    return null;
}

With defer it becomes more bearable indeed, thx @daurnimator ! The 2 extra line costs of var ok and ok = true come out for the current example to the same overall LoC (-1) but at least if additional elses were to come into play it would amortize decently.

pub fn listToBytes(mem: *std.mem.Allocator, maybeNumList: ?[]const Expr) !?[]const u8 {
    if (maybeNumList) |it| {
        var ok = false;
        const bytes = try mem.alloc(u8, it.len);
        defer if (!ok) mem.free(bytes);
        for (it) |expr, i|
            if (expr.is(.NumInt)) |n| { // .is() expands to: switch(expr) { .NumInt => |n| ..., else => ... }
                if (n >= 0 and n <= 255)
                    bytes[i] = @intCast(u8, n)
                else
                    return null;
            } else
                return null;
        ok = true;
        return bytes;
    }
    return null;
}