如何在jshell中的/ set truncation命令中使用选择器？

Question

I am using jshell and want to truncate the very big message displayed on jshell console.

For this, i got the /set truncate command which says:

If the values are too long, then they are truncated when displayed. Use the /set truncation command to set the maximum length shown for a value. If no settings are entered with the command, then the current setting is displayed.

Below are the relevant selector kinds for truncation.

|  
|  The case selector kind describes the kind of snippet.  The values are:
|   vardecl    -- variable declaration without init
|   varinit    -- variable declaration with init
|   expression -- expression -- note: {name}==scratch-variable-name
|   varvalue   -- variable value expression
|   assignment -- assign variable
|  The action selector kind describes what happened to the snippet.  The values are:
|   added     -- snippet has been added
|   modified  -- an existing snippet has been modified
|   replaced  -- an existing snippet has been replaced with a new snippet

Can anybody please suggest the use cases of the case selectors or the action selectors??

Answer 1

want to truncate the very big message displayed on jshell console.

This relies on what type of message do you want to truncate. The case selector in which shall help you decide the type and action selector would help you decide when to do so. eg adding snippets, modifying etc.

How to use selectors in /set truncation command in jshell?

The examples from the same documentation lists out these nicely:

/set truncation mymode 45 expression
/set truncation mymode 0 varinit-modified,replaced

suggest the use cases of the case selectors or the action selectors??

The documentation for defining a feedback mode # Set truncation section :

mymode: /set truncation mymode 100

mymode: /set truncation mymode 300 varvalue

# default truncation
mymode: String big = IntStream.range(0,1200).mapToObj(n -> "" + (char) ('a' + n % 26)).collect(Collectors.joining())
big ==> "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv ... fghijklmnopqrstuvwxyzabcd"

# default truncation
mymode: big + big
$2 ==> "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghi ... yzabcdefghijklmnopqrstuvwxyzabcd"

# we can see the overriden truncation value in the next statement
mymode: big
big ==> "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkl...jklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcd"`