列表元素自增

Question

对于其他语言，列表元素自增是非常容易的，就像:

list1(i) = list1(i) + 1

但对于 tcl，目前我使用:

set temp [lindex $list1 $i];
lset list1 $i [expr $temp + 1];

还有其他方法可以改进/使其更简单吗？

Answer 1

对于 Tcl list，我不确定是否有任何内部命令可以直接增加列表元素的值。

但是，如果您在 Tcl 中通过 dict incr 命令使用字典，则可以做到这一点。

dict incr dictionaryVariable key ?increment?

This adds the given increment value (an integer that defaults to 1 if not specified) to the value that the given key maps to in the dictionary value contained in the given variable, writing the resulting dictionary value back to that variable. Non-existent keys are treated as if they map to 0. It is an error to increment a value for an existing key if that value is not an integer. The updated dictionary value is returned.

set sample { firstName Dinesh lastName S title Mr age 23} 

# This will increase the value of 'age' by 1
puts [ dict incr sample age 2] 

# If any key used which does not exits in the dict, then it will create that key
# assume it's initial value is 0.

puts [ dict incr sample dob ]

输出:

firstName Dinesh lastName S title Mr age 25
firstName Dinesh lastName S title Mr age 25 dob 1

如果您仍然对在列表元素中使用增量感兴趣，那么我们可以编写一个新命令，如下所示，

proc lincr { my_list index { increment 1 } } {
     upvar $my_list user_list
     if { [llength $user_list] <= $index } {
          return -code  error "Wrong list index"
     }  
     lset user_list $index [ expr {[lindex $user_list $index] + $increment} ]
}

set val { 1 2 3 4 } 
lincr val 1 4; # Increasing first index by 4
lincr val 0; #Increasing zeroth index by 1
puts $val