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What is a term for a function that when called repeatedly, has the same effect as calling once?

28

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

naming functions

share|improve this question

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

• 
  
  
  

  
  13
  

  
  
  
  
  
  

  
  
  To the close voter(s): while it is true that 99.999% (rough estimate) of all "name-that-thing" questions are off-topic because they don't have a single, correct, unambiguous, objective answer and the naming is purely subjective and opinion-based, this one does have a single, correct, unambiguous, objective answer, which was given by the OP himself.
  
  – Jörg W Mittag
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Calling it multiple times does have an effect, as there could be other code that changed 'var' in between.
  
  – RemcoGerlich
  4 hours ago
  

  
  
  
  

add a comment | 

28

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

naming functions

share|improve this question

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

• 
  
  
  

  
  13
  

  
  
  
  
  
  

  
  
  To the close voter(s): while it is true that 99.999% (rough estimate) of all "name-that-thing" questions are off-topic because they don't have a single, correct, unambiguous, objective answer and the naming is purely subjective and opinion-based, this one does have a single, correct, unambiguous, objective answer, which was given by the OP himself.
  
  – Jörg W Mittag
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Calling it multiple times does have an effect, as there could be other code that changed 'var' in between.
  
  – RemcoGerlich
  4 hours ago
  

  
  
  
  

add a comment | 

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

naming functions

share|improve this question

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

int var = 0;



void func1()

{

    var = 10;

}

int var = 0;



void func2()

{

    var++;

}

share|improve this question

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

share|improve this question

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

edited 2 hours ago

Erel Segal-Halevi

4681612

edited 2 hours ago

Erel Segal-Halevi

4681612

asked 10 hours ago

WoofasWoofas

39947

asked 10 hours ago

WoofasWoofas

39947

2 Answers
2

active

oldest

votes

65

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.

share|improve this answer

answered 10 hours ago

WoofasWoofas

39947

add a comment | 

19

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.

share|improve this answer

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  I think your definition of idempotency is too narrow, or put another way, you are using the mathematical definition of idempotency, not the programming one. For example, the PUT and DELETE HTTP methods are called idempotent precisely because executing their side-effects multiple times has the same effect as executing them only once. You are saying "idempotency means f∘f = f", whereas in programming, we mean "executing f has the same effect has executing f; f". Note that you can easily transform the second meaning into the former by adding a "world" parameter.
  
  – Jörg W Mittag
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JörgWMittag Idempotency is strictly a mathematical term. In the context of programming, there are no "side effects", but if you were to expand the definition to include this, then a idempotent function and a pure function would mean the same thing. Clearly that isn't the case as a pure function isn't only idempotent, but also has no side effects. As I see it, something is idempotent if you could never receive differing results for the same input after multiple calls. But I suppose we can agree to disagree on that point.
  
  – Neil
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @JörgWMittag, the issue with the term, idempotent, is that it's effectively defined differently in imperative and function programming approaches as purity is assumed for the latter, but not for the former.
  
  – David Arno
  5 hours ago
  

  
  
  
  

add a comment | 

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65

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.

share|improve this answer

answered 10 hours ago

WoofasWoofas

39947

add a comment | 

65

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.

share|improve this answer

answered 10 hours ago

WoofasWoofas

39947

add a comment | 

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.

share|improve this answer

answered 10 hours ago

WoofasWoofas

39947

share|improve this answer

answered 10 hours ago

WoofasWoofas

39947

answered 10 hours ago

WoofasWoofas

39947

answered 10 hours ago

WoofasWoofas

39947

19

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.

share|improve this answer

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  I think your definition of idempotency is too narrow, or put another way, you are using the mathematical definition of idempotency, not the programming one. For example, the PUT and DELETE HTTP methods are called idempotent precisely because executing their side-effects multiple times has the same effect as executing them only once. You are saying "idempotency means f∘f = f", whereas in programming, we mean "executing f has the same effect has executing f; f". Note that you can easily transform the second meaning into the former by adding a "world" parameter.
  
  – Jörg W Mittag
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JörgWMittag Idempotency is strictly a mathematical term. In the context of programming, there are no "side effects", but if you were to expand the definition to include this, then a idempotent function and a pure function would mean the same thing. Clearly that isn't the case as a pure function isn't only idempotent, but also has no side effects. As I see it, something is idempotent if you could never receive differing results for the same input after multiple calls. But I suppose we can agree to disagree on that point.
  
  – Neil
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @JörgWMittag, the issue with the term, idempotent, is that it's effectively defined differently in imperative and function programming approaches as purity is assumed for the latter, but not for the former.
  
  – David Arno
  5 hours ago
  

  
  
  
  

add a comment | 

19

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.

share|improve this answer

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  I think your definition of idempotency is too narrow, or put another way, you are using the mathematical definition of idempotency, not the programming one. For example, the PUT and DELETE HTTP methods are called idempotent precisely because executing their side-effects multiple times has the same effect as executing them only once. You are saying "idempotency means f∘f = f", whereas in programming, we mean "executing f has the same effect has executing f; f". Note that you can easily transform the second meaning into the former by adding a "world" parameter.
  
  – Jörg W Mittag
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JörgWMittag Idempotency is strictly a mathematical term. In the context of programming, there are no "side effects", but if you were to expand the definition to include this, then a idempotent function and a pure function would mean the same thing. Clearly that isn't the case as a pure function isn't only idempotent, but also has no side effects. As I see it, something is idempotent if you could never receive differing results for the same input after multiple calls. But I suppose we can agree to disagree on that point.
  
  – Neil
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @JörgWMittag, the issue with the term, idempotent, is that it's effectively defined differently in imperative and function programming approaches as purity is assumed for the latter, but not for the former.
  
  – David Arno
  5 hours ago
  

  
  
  
  

add a comment | 

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.

share|improve this answer

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

int func1(int var)

{

    return var + 1;

}

share|improve this answer

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

edited 1 hour ago

yoozer8

5721520

edited 1 hour ago

yoozer8

5721520

answered 6 hours ago

NeilNeil

19.9k3567

answered 6 hours ago

NeilNeil

19.9k3567