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Comment by Infernal | Hacker News Reader

It’s not clear to me what the difference in definition is - even reading the CS definition on Wikipedia, both cases reference the mathematical definition. What am I missing?

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In the imperative sense of idempotent, a method is idempotent with respect to system state, not just its arguments.

It's about repeated calls e.g.

    a.f(x).f(x)

results in the same state as

    a.f(x)

Not about repeated application. E.g.

    f(f(x)) = f(x)

Right. If you think about it as a function of the state itself, the 2 definitions agree. If the function is `f(x, state) -> (y, state')`, then f is "imperitively idempotent" when `g(state) = f(fixedX, state).state'` is "mathematically idempotent"

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