Use a function to define an optional parameter

Question

Is it possible to use the return value of a function instead of a specific value as optional parameter in a function? For example instead of:

public void ExampleMethod(int a, int b, int c=10)
{
}

I want something like

private int ChangeC(int a, int b)
{
    return a+b;
}

public void ExampleMethod(int a, int b, int c=ChangeC(a,b))
{
}

No, because the parameters for that method do not exist in that context. You could just use it on the first line of your method: c = c ?? ChangeC(a,b) — Glenn van Acker
– Glenn van Acker, Commented Dec 11, 2019 at 12:22
Please give an example in pseudo code. It is a bit unclear what you want to achieve. — Rob
– Rob, Commented Dec 11, 2019 at 12:23
You could have two overloads of the method - one with three parameters & one with two that calls the first using the results of the function call as the third parameter — PaulF
– PaulF, Commented Dec 11, 2019 at 12:25

MindSwipe · Accepted Answer · 2020-11-12 12:13:06Z

16

No this is not possible. For a parameter to be optional the value must be a compile time constant. You can however overload the method like so:

private int ChangeC(int a, int b)
{
    return a + b;
}

public void ExampleMethod(int a, int b, int c) {}

public void ExampleMethod(int a, int b)
{
    ExampleMethod(a, b, ChangeC(a, b));
}

This way you don't have to deal with nullable value types

edited Nov 12, 2020 at 12:13

answered Dec 11, 2019 at 12:24

MindSwipe

8,0441 gold badge27 silver badges59 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Gleb · Accepted Answer · 2019-12-11 12:29:53Z

8

One of the ways:

private int ChangeC(int a, int b)
{
    return a+b; 
} 

public void ExampleMethod(int a, int b, int? c=null)
{
    c = c ?? ChangeC(a,b);
}

answered Dec 11, 2019 at 12:29

Gleb

1,7711 gold badge13 silver badges24 bronze badges

Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

Is it possible to use the return value of a function instead of a specific value as optional parameter in a function?

No. It is not possible. The C# programming guide on Optional Arguments says:

A default value must be one of the following types of expressions:

a constant expression;

an expression of the form new ValType(), where ValType is a value type, such as an enum or a struct;

an expression of the form default(ValType), where ValType is a value type.

See other answers for alternative solutions.

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Dec 11, 2019 at 12:33

Theraot

41.2k7 gold badges70 silver badges107 bronze badges

Collectives™ on Stack Overflow

Use a function to define an optional parameter

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related