[stringtemplate-interest] "Or" and "And" operators in conditionnal always evaluate both operands ?

[Damien Urruty]

The case I use is the following : 
<if(type.defaultConstructor && type.defaultConstructor.exceptions)>
with the first operand calling the getDefaultConstructor() method on my type object, and the second operand calling getExceptions() on my constructor object, returning a list of types raised byt eh constructor.

If there is no default constructor declared in my type, then the second chunk is still evaluated, and gives me the error given in the previous mail : 

"templateName : no such property or can't access: null attribute"
So what you are saying Sam, is that I could use this conditional (even with the two operand), and this should not raise any error ?

From: sharwell at pixelminegames.com
To: lepilache at hotmail.com; stringtemplate-interest at antlr.org
Subject: RE: [stringtemplate-interest] "Or" and "And" operators in conditionnal always evaluate both operands ?
Date: Thu, 15 Sep 2011 09:02:17 -0500



A condition like “a.b” should always evaluate to false if “a” is null. In StringTemplate, there’s no need to condition it on “a” as well. You should definitely just use this, and if an error is occurring then we should work it out. :) Can you post the exact condition you’re using? <if(a.b)> Sam From: Damien Urruty [mailto:lepilache at hotmail.com] 
Sent: Thursday, September 15, 2011 8:54 AM
To: sharwell at pixelminegames.com; stringtemplate-interest at antlr.org
Subject: RE: [stringtemplate-interest] "Or" and "And" operators in conditionnal always evaluate both operands ? Hi, The problem I am facing is that my conditional is something like :  <if(a && a.b)> Which raises an error in the case a is null (a.b is still evaluated).  By the way, the error is not very explicit : "templateName : no such property or can't access: null attribute". I spent some time finding where the error came from. It is not a question of performance, I was just wondering if this behaviour was normal, I mean if this is by design, or if it was a bug. In my case, I can easily break the if in two separate ifs, so it doesn't really matter. But as in Java the && does not evaluate all the operands if not necessary (the & operator do evaluate each operand), i wanted to know if this behaviour was wanted or not. Maybe this should be discussed, I know it is not very important, or at least it should be mentionned somewhere in the doc ? Thanks for your response Sam, have a nice dayFrom: sharwell at pixelminegames.com
To: lepilache at hotmail.com; stringtemplate-interest at antlr.org
Subject: RE: [stringtemplate-interest] "Or" and "And" operators in conditionnal always evaluate both operands ?
Date: Thu, 15 Sep 2011 08:43:29 -0500Hi Damien, Since the attributes referenced from a StringTemplate should always be pure (no side effects), then there is no semantic difference between evaluating or not evaluating the second argument. Are you facing a significant performance problem due to the second evaluation? Sam From: stringtemplate-interest-bounces at antlr.org [mailto:stringtemplate-interest-bounces at antlr.org] On Behalf Of Damien Urruty
Sent: Thursday, September 15, 2011 8:01 AM
To: stringtemplate-interest at antlr.org
Subject: [stringtemplate-interest] "Or" and "And" operators in conditionnal always evaluate both operands ? Hello, I can see that if we use && and || operands in conditionnals, both operands are always evaluated, even if not necessary. For exemple, I have  :  <if(a && b)>...<endif> In my case, a is null, so it is not necessary to evaluate the second argument, right ? Shouldn't the evaluation stop when such a case is encountered ? It is the same for <if(a || b)> with a not null. Maybe I miss something, thanks for your help. 		 	   		  
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