[stringtemplate-interest] [ST4] How to avoid map key iteration?

[Udo Borkowski]

Hi Ter,

> Hi. my first thought is, don't try to iterate over the object.  
> ...
> <adr:{t|<t.zip> <t.city>}>
:-)

OK, I was trying to make the example as simple as possible, just to show my case. Of cause this simple example could be written as you suggest.

My point is: when writing:

    <adr:{t|<t.zip> <t.city>}>

I don't want to "iterate" over the object but rather pass an argument to the anonymous templates. The "iterate" happens accidently, just because adr also is iterable.


Here the more complete example:

Assume we have this template:

    t1(adr) ::= <<
    <adr.firstname> <adr.lastname>
    <adr.zip> <adr.city>
    >>

With my "bean style" model object I get a result like this:

    ---------
    Joe Smith
    12345 Somecity
   ---------

Most times the format "zip city" is OK. However sometimes it needs to be formatted differently.Therefore I make the second line a parameter with the common case as the default:

    t2(adr,line2={<adr:{a|<a.zip> <a.city>}>}) ::= <<
    <adr.firstname> <adr.lastname>
    <line2>
    >>

This way I can still call the template like this most of the time:

    <t2(adr=p)>

and when a different 2nd line format is needed, I pass it in:

    <t2(adr=p,line2={<adr:{a|<a.city>, <a.zip>}>})>

In this example the result would be:

    ----------
    Joe Smith
    Somecity, 12345
    ----------

This all works fine with the bean-style model object. 

However when I switch to a model object that extends a Map class things break and I get an error like:

    no such property or can't access: java.lang.String.zip 


I hope this somewhat lengthy example make things more clearer.


I guess from a language design point of view I would provide different constructs for the "iterate" vs. "pass argument to anonymous template" case, e.g.

    <adr:{…}>  // the "iterate" case, i.e. "anything iterable" is used as an iterator, as now

    <adr::{…}> // the "pass arg" case, i.e. don't handle iterables differently, just pass in to anon template


Udo


On 11.02.2011, at 17:39, Terence Parr wrote:

> Hi. my first thought is, don't try to iterate over the object.  
> 
> <adr.zip> <adr.city>
> 
> is same as:
> 
> <adr:{t|<t.zip> <t.city>}>
> 
> Ter
> On Feb 11, 2011, at 5:45 AM, Udo Borkowski wrote:
> 
>> Hi,
>> 
>> is there any way to prevent the "iteration" over map keys when using a template like <m:{t|…}> (m may be a map or a simple object)?
>> 
>> Details:
>> 
>> I am using a template like this:
>> 
>> writeAddress(adr) ::= <<
>> ...
>> <adr:{t|<t.zip> <t.city>}>
>> ...
>> >>
>> 
>> adr represents an "Address" with properties "street", "zip", "city" etc.
>> 
>> Initially this was implemented by a bean-style model class Address. Everything worked as expected.
>> 
>> Now I changed the model class to a more "dynamic" implementation by using a Map. I.e. "zip", "city", etc. are now keys in the map, mapping to their resp. values.
>> 
>> Expressions like this:
>> 
>> <a.zip>
>> 
>> still work fine, but 
>> 
>> <adr:{t|<t.zip> <t.city>}>
>> 
>> runs into an error: 
>> 
>> no such property or can't access: java.lang.String.zip
>> 
>> This is because the new model instance "accidentally" is a Map and the expression now iterates over the keys of the map ("zip" being the first).
>> 
>> How can this iteration be avoided?
>> 
>> 
>> Udo
>> 
>> 
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> 
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