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From "Pascal Proulx (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FREEMARKER-107) Hash expansion to macro arguments (Python **kwargs style)
Date Wed, 21 Nov 2018 18:34:00 GMT
Pascal Proulx created FREEMARKER-107:
----------------------------------------

             Summary: 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


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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