I'd like to discuss a strange behaviour (already mentionned sometimes, but without any
concluding point, imho), and to make a
proposal.
When velocimacro.context.localscope is false, a macro may implicitely change the
actual value of its arguments by changing some
external variable implied in their calculation.
This is due to the fact that each time a non-constant argument is evaluated in a
macro, it is re-evaluated with the global context
that may have been changed by the same macro.
For instance, as shown in example 1, if a #foreach or a #set directive inside a macro
uses a reference name similar to the name of a
reference passsed to the macro, then the actual value of the parameters may also
change in the same time.
---------------------
## Example 1 :
## outputs "1 ! a b c" instead of expected "1 1 1 1 1"
#macro (test $arg)
$arg ## -> 1
#set($i = '!')
$arg ## -> !
#foreach ($i in ['a','b','c'])
$arg ## -> a b c
#end
#end
#set($i = 1)
#test($i) ## outputs "1 ! a b c" instead of expected "1 1 1 1 1"
---------------------
This may be seen as a small side effect, but it can lead to very ankward behaviours in
some situations... especially when dealing
with macro recursions.
---------------------
## Example 2 : (partial)
#macro (disp_node $node)
#foreach ($child in $node.children())
$child.name is a child of $node.name
## ^^^^^^^^^^ (I hate proportional fonts)
## "$node.name" evaluate to (external) "$child.name", which equals (internal)
"$child.name"
## so for a basic tree (grandparent-parent-grandson) we get the output "grandson is
a child of grandson"
#disp_node($child)
#end
#end
---------------------
This recursion problem should also be solved if #foreach directives avoided to store
their working variables in the global context,
but it's another point.
I finally made it out for my personal stuff, by the mean of two or three dreadful
workarounds, but here is my point :
Why couldn't macro directives only evaluate once their arguments at the moment
they are called and save them in their local
context ?
This sounds too simple... do I miss something ?
As shown in example 3, only vicious minds (like mine here, for a didactic purpose) may
try to exploit constructively this behaviour.
Otherwise, it's rather strange (and time consuming) to re-evaluate arguments each time.
---------------------
## Example 3 : outputs "hello folks"
#macro (print_twice $value)
$value $value
#end
#set ($myarray = ["hello","folks"])
#print_twice($myarray.remove(0))
---------------------
Depending on the followup, I'd be glad to try to contribute attenant patches.
Thanx for reading up to that point.
And last but not least, thanx a lot to the support team.
Sincerely,
CloD
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