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Posted 28 Mar 2011

# Call Functions Until One Meets Condition

, 1 May 2012 CPOL
 Rate this:
Call a series of functions until the return value meets a condition without a chained-if or short-circuiting.

Thanks to cechode for inspiring this tip/trick. Suppose you have the following functions:

```bool Step1()
{
return true;
}
bool Step2(int val1, int val2)
{
return val1 == val2;
}
bool Step3()
{
MessageBox.Show("I will be reached.");
return false;
}
bool Step4()
{
throw new Exception("This should be impossible!");
}```
```Function Step1() As Boolean
Return True
End Function

Function Step2(ByVal val1 As Integer, ByVal val2 As Integer) As Boolean
Return val1 = val2
End Function

Function Step3() As Boolean
MessageBox.Show("I will be reached.")
Return False
End Function

Function Step4() As Boolean
Throw New Exception("This should be impossible!")
End Function```

If you want to execute each of those in sequence until one returns `false`, you can do the following:

```new Func<bool>[]
{
Step1,
// You can use a lambda to wrap a function with a different signature.
() => Step2(1, 1),
Step3,
Step4,
// You can use a lambda to avoid the use of a function.
() => 0 == 1
}.Any((step) => !step());```
```' This is achieved fairly easily in VB.NET
Select Case False
Case Step1()
Case Step2(1, 1)
Case Step3()
Case Step4()
Case 0 = 1
End Select
```

Note that the result need not be `true `or `false`; it can be any value or condition. I could, for example, process each function until the result is an integer greater than or equal to `5` (Note that in VB.NET the `Select Case` statement can't handle conditions, it can only handle values, so the code is modified accordingly):

```// This assumes each "Step" function from above returns an int rather than a bool.
new Func<int>[]
{
Step1,
() => Step2(1, 1),
Step3,
Step4,
() => 0 + 1
}.Any((step) => step() >= 5);```
```' VB.NET.
Dim steps() As Func(Of Integer) =
{
Function() Step2(1, 1),
Function() 0 + 1
}

' We test against a condition rather than a value.
steps.Any(Function([step]) [step]() >= 5)
```

The condition `>= 5` is a very short one, so this won't save you any typing over the short-circuiting technique shown below. However, it would save you some typing for longer conditions. Specifying the condition only once rather than for each value also reduces the probability that you will make a mistake when typing. And if you change the condition later on, you only have to change the condition in one place rather than many. Here is the short-circuiting approach, which leads to duplicated code:

```// Don't do this.
if (Step1() >= 5 ||
Step2(1, 1) >= 5 ||
Step3() >= 5 ||
Step4() >= 5 ||
0 + 1 >= 5)
{ }```
```' VB.NET. Don't do this.
If Step1() >= 5 OrElse
Step2(1, 1) >= 5 OrElse
Step3() >= 5 OrElse
Step4() >= 5 OrElse
0 + 1 >= 5 Then
End If
```

While shorter for this example (due to the short condition), this code also has the maintenance problems and higher probability of human error explained above.

## Share

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• Managing Your JavaScript Library in ASP.NET (if you work with ASP.net and you don't read that, you are dead to me).

• Graduated summa cum laude with a BS in Computer Science.

• Wrote some articles and some tips.

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 My vote of 5 Pravin Patil, Mumbai26-Jun-12 22:02 Pravin Patil, Mumbai 26-Jun-12 22:02
 Very nice trick zenwalker19857-Jun-12 6:37 zenwalker1985 7-Jun-12 6:37
 My vote of 5 thatraja1-May-12 19:52 thatraja 1-May-12 19:52
 Re: Definitely makes more sense if you are doing an operation th... Andrew Rissing30-Mar-11 4:42 Andrew Rissing 30-Mar-11 4:42
 Definitely makes more sense if you are doing an operation that is more complex.
 Re: Done updating. AspDotNetDev29-Mar-11 11:05 AspDotNetDev 29-Mar-11 11:05
 Re: Cool, I'll let you know once I'm finished making updates. I ... AspDotNetDev29-Mar-11 7:26 AspDotNetDev 29-Mar-11 7:26
 Re: I'll keep an eye out for the update, because at this point I... Andrew Rissing29-Mar-11 6:46 Andrew Rissing 29-Mar-11 6:46
 Reason for my vote of 5 Makes you think, and then you are go... FDW24-Jun-11 0:57 FDW 24-Jun-11 0:57
 how do i move my alternate from a pending state? ( been like... cechode29-Mar-11 5:33 cechode 29-Mar-11 5:33
 Re: It requires approval from another person. Looks like somebod... AspDotNetDev29-Mar-11 7:25 AspDotNetDev 29-Mar-11 7:25
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