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I saw this in my generated GSP pages. What does the ? mean?
<g:textField name="name" value="${phoneInstance?.name}" /> 
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Yes, the "?:" operator will return the value to the left, if it is not null. Else, return the value to the right. "Yes, the "?:" operator will return the value to the left, if it is not null." - That is incorrect.
?. is a null safe operator which is used to avoid unexpected NPE.
In Groovy we can do this shorthand by using the null safe operator (?.). If the variable before the question mark is null it will not proceed and actually returns null for you.
Groovy Servers Pages (or GSP for short) is Grails' view technology. It is designed to be familiar for users of technologies such as ASP and JSP, but to be far more flexible and intuitive.
It's the "Safe Navigation Operator", which is a Groovy feature that concisely avoids null pointer exceptions. See http://docs.groovy-lang.org/latest/html/documentation/index.html#_safe_navigation_operator
In this case, if phoneInstance is null, then it doesn't try to get the name property and cause a NPE - it just sets the value of the field tag to null.
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