Unexpected switch command behavior in TCL

Question

I am trying to run the below switch block using TCL. I am expecting the output to be 10 based on how the switch statement works. But the output comes out to be Default. I am not what's the explanation behind that and how I can fix it.

set a 10
set data 10

switch $data {
    $a {
        puts "10"
    }
    default {
        puts "Default"
    }
}

The output is:

Default

Answer 1

In tcl, the string enclosed in {} is literal. The variables in the string is not substituted. The same rule applies to the statements of the {} blocks passed to if/for/switch commands.

So in your case, $a is a literal string, not 10, for the switch command.

You may re-write your switch block as following thus $a is substituted to 10 before passed to switch command.

switch $data [list \
    $a {
        puts "10"
    } \
    default {
        puts "Default"
    } \
]