What does this Zig snippet output?

1const std = @import("std");
2pub fn main() void {
3    const T = struct { a: u32 = 10, b: u32 = 20, c: u32 = 30 };
4    const obj = T{};
5    std.debug.print("{d}\n", .{@field(obj, "b")});
6}