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https://issues.apache.org/jira/browse/FREEMARKER-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16952949#comment-16952949
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Pascal Proulx commented on FREEMARKER-107:
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I understand. I tried to avoid needless map copies (and my defaults had only
constants, as you can tell). I like your idea of detecting .args references,
but it could just be specified in the documentation that if you need it in
interpreted code, you can just do a <#local dummy = .args/> beforehand outside
of it.
Otherwise the only other way I can see this (in general Freemarker language, I
emulated this manually) is using a built-in that does map copies, so it can be
done on demand, roughly (not sure if .locals is appropriate or exactly right):
{code:java}
<#macro m4 a=3 b=3 extra...><#local args = .locals?hash_copy + extra><#-- ...
--></#macro>{code}
Obviously it would be nicer to not have to do that, but it is still simpler
than what I had (only one extra line), and you can decide if you want the
catch-all or not.
I guess I should point out I used a hacked hash copy utility in some other
parts as well, like an advanced built-in. The only problem was not preserving
the original map type in cases of maps coming from context (LinkedHashMap,
TreeMap, etc.), but it could be understood that it always makes a simple hash
or something. If there is any interest in that (sorry, too many suggestions :P).
> Hash expansion to macro arguments (Python **kwargs style)
> ---------------------------------------------------------
>
> Key: FREEMARKER-107
> URL: https://issues.apache.org/jira/browse/FREEMARKER-107
> Project: Apache Freemarker
> Issue Type: New Feature
> Components: engine
> Affects Versions: 2.3.28
> Reporter: Pascal Proulx
> Priority: Major
>
> Hello,
> We heavily rely on Freemarker macros to build a helper template API, but have
> had to make large workarounds for passing contents of hashes as macro
> arguments, for several years. (In truth I should have made this ticket much
> sooner!)
> It would help greatly simplify our work to have hash expansion to macro
> arguments, like this:
> {code:java}
> <#macro myMacro arg1 arg2 arg3="value3">...</#macro>
> <#assign myHash = {"arg1":"value1", "arg2":"value2"}>
> <@myMacro **myHash/><#-- the hash contents are passed as parameters, instead
> of the hash itself -->
> {code}
> This exists in Python:
> {code:java}
> def test_var_args_call(arg1, arg2, arg3):
> pass
> kwargs = {"arg3": 3, "arg2": "two"}
> test_var_args_call(1, **kwargs)
> {code}
> Essentially the hash contents fill in any arguments not explicitly specified.
> For the case where arguments are specified in addition to the hash, you may
> need to decide on a good syntax, e.g.:
> {code:java}
> <@myMacro arg1="value1" **myHash/>{code}
> This example doesn't have much precedent in freemarker syntax but is fairly
> understandable.
> Although we don't need it nearly as much, the same could be done with lists
> and function arguments:
> {code:java}
> <#function myFunc arg1 arg2>...</#function>
> <#assign myList = ["val1", "val2"]>
> ${myFunc(*myList)}
> <#assign myList = ["val2"]>
> ${myFunc("val1", *myList)}
> {code}
> Again similar to Python:
> {code:java}
> def test_var_args_call(arg1, arg2, arg3):
> pass
> args = ("two", 3)
> test_var_args_call(1, *args)
> {code}
> You might want this for consistency, although in practice the hash expansion
> will be many times more useful to us.
> If there's a lack a manpower I could try to see what I can do digging into
> the source, but wanted to bring this up for discussion first. It doesn't
> appear hard to implement to dump a hash into the macro args map, but there is
> defining the syntax.
> We use Freemarker 2.3.28 at the moment.
> Thank you
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