iif()


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Postby Ursego » 19 Feb 2013, 21:29

The function iif(<boolean expression>, <1st value>, <2nd value>) returns the 1st value if the boolean expression is TRUE; otherwise, it returns the 2nd value.

It works similar to the ternary operator in C/C++/C#/Java (<cond> ? <if true> : <if false>; ) and the IIf function in Visual Basic (as you can read there, "IIf" stands for "Internal If"):

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ls_greeting = iif(lc_sex = "M", "Mr", "Ms")

This approach is very convenient - it helps to keep scripts shorter by avoiding an unnecessary if...else construction. Each use of iif() removes 4 extra lines from the script. That's how the fragment would be looking like without iif():

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if lc_sex = "M" then
   ls_greeting = "Mr"
else
   ls_greeting = "Ms"
end if

CAUTION, especially if you came from C/C++/C#/Java! If you pass an expression as the 2nd or 3rd argument, that expression is evaluated before being sent to the function (no matter what the result of the Boolean expression is), so DON'T USE iif() as a protection against things like zero divide or reading from a not-existing row in a DataWindow (as you would do using the ternary operator in a language with C-like syntax):

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ll_result = iif(ll_2 <> 0, ll_1 / ll_2, 0) // runtime error if ll_val_2 = 0!!!
ls_name = iif(ll_row > 0, dw_test.object.name[ll_row], "No name") // runtime error if ll_row = 0!!!


HOW TO ADD THE FUNCTION TO THE APPLICATION

1. Save the file spy.pbl on your hard disk (in the folder where the PBLs are stored). The function is in that PBL.
2. Add it to your application's library list.

The function is overloaded for the following datatypes: string, long, decimal, date, time, datetime, PowerObject. To see the overloads, open the function in the "Edit Source" mode. If you are surprised that a global functions is overloaded then read here.
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Ursego
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