Question about D-Flip Flop

[kqian]

According to the book D-Flip flop doesn't change output until the clock edge rises. So if I want to read a value from a register that means DFF has to wait until the clock is on rising edge before it can return the output. Is that so?

[ybakos]

Sort of. You can read from a register at any time. But to change the value in the register, and then to read that new value, you must wait until the next clock cycle.

[kqian]

What is stopping me from loading and reading in the same cycle? It seems the wrong output could be passed this way.