[ nice-Bugs-926524 ] compiler detecting tests for nullness

Bugs item #926524, was opened at 2004-03-31 16:23
Message generated for change (Comment added) made by fbarber
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=112788&aid=926524&group_id=12788

Category: None
Group: None
Status: Closed
Resolution: None
Priority: 5
Submitted By: Francis Barber (fbarber)
Assigned to: Nobody/Anonymous (nobody)
Summary: compiler detecting tests for nullness

Initial Comment:
The compiler complains about the following code:

String s;
s = gv.docString() != null ? gv.docString() : "null";

The error is:

The value if(`!=`(gv.docString(), null))
gv.docString()
else
"null"
 cannot be assigned to s because it might be null.

However, the following code compiles fine:

void bar(?String arg) {
    String s;
    s = arg != null ? arg : "null";
}

Thanks,
Frank.

----------------------------------------------------------------------

>Comment By: Francis Barber (fbarber)
Date: 2004-04-01 11:06

Message:
Logged In: YES 
user_id=684961

Sorry, I clearly didn't think this through properly!

Are there any issues with threads here?  Is there a chance 
that a variable could be altered by another thread?

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Comment By: Arjan Boeijink (arjanb)
Date: 2004-03-31 19:24

Message:
Logged In: YES 
user_id=688815

This is not a bug because the compiler doesn't know whether 
the second call of gv.docString() returns the same value as 
the first.

There's a feature request for this issue: 
https://sourceforge.net/tracker/index.php?
func=detail&aid=671444&group_id=12788&atid=362788

In this case you can avoid the error using the 'option' or:

s = gv.docString() || "null";

this is about the same as:

let temp = gv.docString();
s = (temp != null) ? temp : "null"

Arjan

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=112788&aid=926524&group_id=12788


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