问题
Say I have the following structure:
package require Itcl
itcl::class AAA {
private variable m_list {}
constructor {} {
fill m_list list
}
}
How to get a reference on the m_list in order to write
foreach elem $reference {.......}
Consider that list is really big and I don't want to copy it!
回答1:
Tcl variables use copy-on-write semantics. You can safely pass a value around, assigning multiple variables to it, without worrying about it taking up more space in memory.
For example
set x {some list} ;# there is one copy of the list, one variable pointing at it
set y $x ;# there is one copy of the list, two variables pointing at it
set z $y ;# there is one copy of the list, three variables pointing at it
lappend z 123 ;# there are two copies of the list
;# x and y pointing at one
;# z pointing at the other
;# which is different from the first via an extra 123 at the end
The above code will result in two giant lists, one with the original data that both x any y point at, and one with the extra element of 123 that only z points to. Prior to the lappend statement, there was only one copy of the list and all three variables pointed at it.
回答2:
Here is how to get a reference on the member of a class:
package require Itcl
itcl::class AAA {
public variable m_var 5
public method getRef {} {
return [itcl::scope m_var]
}
}
AAA a
puts [a cget -m_var]
set [a getRef] 10
puts [a cget -m_var]
来源：https://stackoverflow.com/questions/6951626/how-to-get-a-reference-on-the-itcl-class-member-variable