Htydjtk

A function that fulfills this criteria is

int var = 0;



void func1()

{

    var = 10;

}

As you can see, calling fun1 10 times has the same effect as calling it once (assigns 10 to var)

A function that does not fulfill this criteria is

int var = 0;



void func2()

{

    var++;

}

Calling func2 10 times results in var being assigned a different value as compared to calling func2 once

This type of function / operation is called Idempotent

Idempotence (UK: /ˌɪdɛmˈpoʊtəns/,[1] US: /ˌaɪdəm-/)[2] is the property of certain operations in mathematics and computer science whereby they can be applied multiple times without changing the result beyond the initial application.

The precise term for this is as Woofas mentions, is idempotence. I wanted to add that while you could call your func1 method idempotent, you could not call it a pure function. The properties of a pure function are two: it must be idempotent and it must not have side effects, which is to say, no mutation of local static variables, non-local variables, mutable reference arguments or I/O streams.

The reason I mention this is that a idempotent function with side effects is not good either, since technically idempotent refers to the return ouptut of the function, and not to the side effects. So technically your func2 method is idempotent, as the output doesn't change according to the input.

You most likely want to specify that you want a pure function. An example of a pure function might be as follows:

int func1(int var)

{

    return var + 1;

}

More reading can be found here.

In physics I've heard this referred to as a projection:

a projection is a linear transformation P from a vector space to itself such that P² = P. That is, whenever P is applied twice to any value, it gives the same result as if it were applied once (idempotent).

Graphically, this makes sense if you look at a cartoon of a vector projection:

In the picture, a₁ is the projection of a on to b, which is like the first application of your function. Subsequent projections of a₁ on to b give the same result a₁. In other words, when you call a projection repeatedly, it has the same effect as calling it once.

Fair warning: I've never heard this used outside of physics, so unless you've got of those types on your team you might confuse everyone.

I would call it a stateless function. While the term idempotent is correct, I think stateless would be more widely understood.