Discussion

This Mockingbird function accepts between one and three input expressions:

• The first parameter is the conditional expression, a Mockingbird expression that will be evaluated in a boolean context. If only this parameter is provided and it evaluates to true, the result of evaluating the conditional expression in the object context will be returned, while nil is returned if the single parameter evaluates to false.

• An optional true return value, which is returned by the function if the conditional evaluates to true.

• An optional false return value, which is returned if the conditional evaluates to false. If this parameter is omitted and the conditional evaluates to false, nil is returned.

Expression usage

Note: This function is exposed to the Mockingbird environment with a name that differs from that of its implementing method:

 ^if($year -LT 2015|Past|Present or future?)

The expression above would return the string “Past” if the conditional expression $year -LT 2015 evaluates to true; otherwise, the string “Present or future?” is returned.

In the following expression:

 ^if($year -EQ 2015|This Year)

the string “This Year” is returned if $year equals 2015; if $year is any other value, nil is returned.

Finally, assume $cartItems refers to an array:

 ^if($cartItems.count)

if $cartItems.count evaluates to true in a boolean context (i.e., if $cartItems.count is non-zero), the object value of $cartItems.count is returned. Otherwise, if $cartItems.count is 0, nil is returned.

So, if $cartItems contains 7 items, the expression ^if($cartItems.count) would yield the result 7. But if the array containeds no items, nil would be returned.