[stringtemplate-interest] wrapping long lines in ST expressions

Sun May 28 11:45:24 PDT 2006

Hi,

I'm in need of proper line wrapping as I'm generating some big static  
arrays of ints.  We need to come up with a nice mechanism that is  
easy and general.  The easiest thing would probably be a lineLength  
parameter to either toString() or as a property of STs or STGs.  ST  
would need to insert a \n before spitting out an expression if the  
prior output on that line is over the threshold.  You want the output  
to break in between expressions so that you avoid splitting output  
constructs unnecessarily, but the common case is probably a single  
attribute expression that has multiple things spit out like an array  
of ints.

Can people think of common uses for wrapping other than lists and such?

Do we need an indentation parameter also?

int[] a = { a, b,
             c, d };

Those spaces before the "c" (sizeof("int[] a = { ")) are what I'm  
talking about.  Here is the generating template:

int[] a = { <elements; indent="            ", separator=", "> };

Those option values can actually template expressions and here is a  
case where we need length() operator.  If the "int" is a variable

<type>[] a = { <elements; indent={<length(type+"            ")>},  
separator=", "> };

which would mean I would need to interpret numeric strings as how  
many spaces?  Hmm...not good.  Also length should be how many  
elements not length in char probably.  How do we deal with variable  
length indentation?  Perhaps we have indent and relativeIndent.   
relativeIndent indents from position of expression start on first line.

There is another issue:  Where do I store the current char count for  
current line?  Can't store in the ST objects as they can be contained  
in multiple other templates and may get examined multiple times to  
display different things.  Seems like the actual invocation of the  
toString() method needs to track the line count for that particular  
execution.  I'll have to create a mutable Integer I guess and pass  
that printing context around to the write() routines.  Perhaps that  
will be a useful thing in general.  I have trouble removing blank  
lines sometimes as I don't know the overall count of char for the  
current line.  Oh, doh!  I have AutoIndentWriter already that knows  
about newlines for indentation...I wonder if we can simply handle  
this with a parameter to the constructor.  Currently, toString() calls:

		StringTemplateWriter wr = group.getStringTemplateWriter(out);

which can be set with:

	/** Specify a StringTemplateWriter implementing class to use for
	 *  filtering output
	 */
	public void setStringTemplateWriter(Class c) {
		userSpecifiedWriter = c;
	}

Revisiting multiple expressions per line:

public void foo(<args; separator=", ">) throws <excepts; separator=", ">
{
	<body>
}

where should it break?  Presumably in between the expressions rather  
than in the middle of one of the expr.  That might be too hard.  The  
output writer sees "public void foo(" then each arg intermixed with  
write(", ") then ") throws " then the excepts elements intermixed  
with ", ".  The write doesn't know anything about literals, intra  
expression and inter expression locations.  Hmm...can't predict the  
future anyway...we don't know that the excepts are coming.

Ok, I think i've convinced myself that a simple char count and  
threshold will do the trick.  Hooray!

Wait, what if you want lines to wrap more tightly for some  
expressions?  Do we need an arg on expressions like

int[] a = { <elements; width=40, separator=", "> };

Hmm...I could store the option in the ASTExpr object like I do for  
indentation and separator.  Well, I don't need it now; agile mindset  
says leave til later ;)

Wow...did I *finally* find a need for more options thus validating my  
complicated <expr; option=value> notation? ;)

Ter
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