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From Dániel Dékány (Jira) <j...@apache.org>
Subject [jira] [Commented] (FREEMARKER-107) Hash expansion to macro arguments (Python **kwargs style)
Date Mon, 07 Oct 2019 20:33:00 GMT

    [ https://issues.apache.org/jira/browse/FREEMARKER-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16946202#comment-16946202
] 

Dániel Dékány commented on FREEMARKER-107:
------------------------------------------

Regarding the argument order, as I wasn't very clear there... The {{?spread_args}} of course
must appear directly after the directive name, and thus before the arguments. What I meant
is that if for example you have catch-all arguments like {{otherArgs}} in {{<#macro a
b otherArgs..>}}, and then you list {{otherArgs}}, then the "spreaded" arguments will be
before the normal arguments. This is because the spread-arguments are applied first, and the
normal arguments after that (so that you can override a "spread" argument value with a normal
argument value).

> 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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