Switch statement and hash table

[markdjones82]

All,

I had a question in regards to the switch statement and hash tables.  I know with a switch statement you can do an array like so

$a = 21, 38, 6

switch ($a)

{ 1 {"The color is red."}

2 {"The color is blue."}

3 {"The color is green."}

4 {"The color is yellow."}

5 {"The color is orange."}

6 {"The color is purple."}

7 {"The color is pink."}

8 {"The color is brown."} }

I actually have found an example that I use to evaluate a hash table based on the $_.name value

$myHash = @{}

$myHash["a"] = 1

$myHash["b"] = 2

$myHash["c"] = 3

switch ($myhash.GetEnumerator())

{ {$_.name -like ‘*a*’ } {"It is a"} }

What I want to understand is how does the curly braces know to do a comparison on the $_.name variable?  How come you don't have to use the Where statement?  I didn't find any documentation on the swtich statement that went over hash tables.  IS there an advanced guide for powershell on syntax for things like this?

Also, is there a good powershell forum out there?  google only shows technet and I'm not a big fan of that format. 

[LucD]

The trick is in the GetEnumerator method that is called.

Through that method the Switch doesn't see a hash table, but a simple object that has a Name and a Value property.

You can check by doing

$myhash.GetEnumerator() | Get-Member

I hope that didn't confuse you more :smileygrin:

[markdjones82]

Gotcha, now on that note, if you pass an object to the switch statement, how does it know to evaluate $_.name?  Don't you need a where statement in there?  Is it hte curly braces that is used to evaluate that?

[markdjones82]

I think i've got it now.  I think it makes more sense here if I break it down.  So you can do a script block for Switch to evaluate if true and if you have an object you can do "object -eq "string" " and powershell knows to evaluate and return true?

Man I don't think I could figure out that logic on my own :smileyplain:

$myhash.GetEnumerator() | where {$_.name -eq "c"
}

Name                           Value
----                           -----
c                              3

$hash = $myhash.GetEnumerator() | where {$_.name -eq "c"}
$hash

Name                           Value
----                           -----
c                              3

$hash.Name
c

$hash.Name -eq "c"

True

[LucD]

That is correct.

Have a look at the section about the Switch statement in Tobias's free ebook.

It explains all the possibilities rather well.

[markdjones82]

Excellent that looks like a good resource!

[LucD]

It is, a high quality document (and free).