[stringtemplate-interest] need a null value for arguments?

[Udo Borkowski]

BTW: ST4 already has the null feature, sort of ;)

Just write:

main() ::= <<
	<t(null)>
>>

and t will get a null (as the identifier null is not defined).

However you will get a warning logged to the console: 

	context [/main] 1:3 attribute null isn't defined

You can easily get rid of this warning by appending a parameter called "null" to your template:

main(null) ::= <<
	<t(null)>
>>

This "null" parameter only needs to be add to the "root" template and can be used in any template call.



Even though this does work I still favor having a "real" null literal :)


Udo


On 01.08.2011, at 22:58, Sam Harwell wrote:

> Adding “undefined” seems pointless, since you can already get that by simply omitting an argument.
>  
> Due to the following expression, it seems reasonable to add a null constant with the value null:
> <t; null="stuff">
>  
> Sam
>  
> From: stringtemplate-interest-bounces at antlr.org [mailto:stringtemplate-interest-bounces at antlr.org] On Behalf Of Udo Borkowski
> Sent: Monday, August 01, 2011 3:04 PM
> To: Terence Parr
> Cc: stringtemplate-interest List
> Subject: Re: [stringtemplate-interest] need a null value for arguments?
>  
> Also: to avoid confusion with the Java null maybe call the constant 'undefined'?
> 
> I was kind of thinking that it should be null because it has the same semantics as passing all in to add().
>  
> Actually this is not the case as you can see in the following test case. That's why I thought mixing "null" und "undefined" isn't such a good idea.
>  
> BTW: in the implementation the "undefined" literal should probably get the value ST.EMPTY_ATTR  rather than null.
>  
>  
> public class UndefinedOrNullTest extends BaseTest {
>        @Test
>        public void testUndefinedParameter() throws Exception {
>               writeFile(tmpdir, "t.stg", "t(s=\"world\") ::= <<\nHello <s>\n>>");
>               String path = tmpdir + "t.stg";
>  
>               STGroup group = new STGroupFile(tmpdir + "/t.stg");
>               ST st = group.getInstanceOf("t");
>               String s = st.render();
>               Assert.assertEquals("Hello world", s);
>        }
>       
>        @Test
>        public void testNullParameter() throws Exception {
>               writeFile(tmpdir, "t.stg", "t(s=\"world\") ::= <<\nHello <s>\n>>");
>               String path = tmpdir + "t.stg";
>  
>               STGroup group = new STGroupFile(tmpdir + "/t.stg");
>               ST st = group.getInstanceOf("t");
>               st.add("s", null);
>               String s = st.render();
>               Assert.assertEquals("Hello ", s);
>        }
> }
>  
>  
> Udo
>  
> On 01.08.2011, at 21:33, Terence Parr wrote:
> 
> 
> 
> On Aug 1, 2011, at 7:10 AM, Udo Borkowski wrote:
> 
> 
> Not sure about the semantic of null.
>  
> E.g. assume you have this template
>  
> t(s="world") ::= "Hello <s>"
>  
> What will
>  
> <t(null)>
>  
> render?
>  
> a) "Hello " (i.e. same as <t("")>)
> b) "Hello world" (i.e. same as <t()>)
> 
> I would assume it would render this one since the parameters missing.
> 
> 
> c) "Hello null"
> d) something else?
>  
>  
> Also: to avoid confusion with the Java null maybe call the constant 'undefined'?
> 
> I was kind of thinking that it should be null because it has the same semantics as passing all in to add().
> 
> Ter
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> stringtemplate-interest mailing list
> stringtemplate-interest at antlr.org
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>  

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