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Choose

Choose ( criterion ; value {; value2 ; ... ; valueN} ) -> Function result

ParameterTypeDescription
criterionBoolean, Integer🡒Value to test
valueExpression🡒Possible values
Function resultExpression🡐Value of criterion

Description​

The Choose command returns one of the values passed in the value1, value2, etc. parameters depending on the value of the criterion parameter.

You can pass either a Boolean or Number type in the criterion parameter:

  • If criterion is a Boolean, Choose returns value1 if the Boolean equals True and value2 if the Boolean equals False. In this case, the command expects exactly three parameters: criterion, value1 and value2.
  • If criterion is an integer, Choose returns the value whose position corresponds to criterion. Be careful, numbering of the values begins with 0 (the position of value1 is thus 0). In this case, the command expects at least two parameters: criterion and value1.

The command accepts all types of data for the value parameter(s), except for pictures, pointers, BLOBS and arrays. Nevertheless, you need to make sure that all the values passed are of the same type, 4D will not carry out any verification on this point.

If no value corresponds to criterion, Choose returns a “null” value with respect to the type of the value parameter (for example, 0 for a Number type, “” for a String type, and so on).

This command can be used to generate concise code that replaces tests of the “Case of” type that take up several lines (see example 2). It is also very useful in places where formulas can be executed: query editor, application of a formula, quick report editor, column calculated in a listbox, and so on.

Warning: The Choose command evaluates each value parameter before its execution. It means that:

  • if value is a dynamic expression that causes side effects (update of a counter, modification of any kind), these effects will happen in all cases;
  • if a value parameter is an invalid expression, Choose will return an error in all cases. For example, the following code will return an error:
 $res:=Choose(True;"red1";"blue"+2) //error

Example 1​

Here is an example of the typical use of this command with a Boolean type criterion:

 vTitle:=Choose([Person]Masculine;"Mr";"Ms")

This code is strictly equivalent to:

 If([Person]Masculine)
    vTitle:="Mr"
 Else
    vTitle:="Ms"
 End if

Example 2​

Here is an example of the typical use of this command with a Number type criterion:

 vStatus:=Choose([Person]Status;"Single";"Married";"Widowed";"Divorced")

This code is strictly equivalent to:

 Case of
    :([Person]Status=0)
       vStatus:="Single"
    :([Person]Status=1)
       vStatus:="Married"
    :([Person]Status=2)
       vStatus:="Widowed"
    :([Person]Status=3)
       vStatus:="Divorced"
 End case