Vista - Checking whether a type is loaded _efficiently_?

Does anyone have any thoughts on how to test whether a type is available
without attempting to create an instance of it?

Alex K. Angelopoulos [MVP] wrote:
> Does anyone have any thoughts on how to test whether a type is
> available without attempting to create an instance of it?

This is pretty fast:

function IsTypeLoaded([string]$typeName, [string]$assemblyName) {
foreach ($asm in [AppDomain]::CurrentDomain.GetAssemblies()) {
if ($asm.GetName().Name -eq $assemblyName) {
if ($asm.GetType($typeName) -ne $null) {
return $true
}
}
}
return $false
}

IsTypeLoaded 'System.Data.DataSet' 'System.Data'

You can do this:

$typename = "system.datetime"
[appdomain]::currentdomain.getassemblies() | % {$_.gettypes()} | ?
{$_.fullname -match $typename}| ft fullname, module -a

If you want an exact match, use "-like" instead of "-match".

Hope that helps,
Jacques

"Alex K. Angelopoulos [MVP]" <aka@online.mvps.org> wrote in message
news:%23XUOTVMtGHA.1956@TK2MSFTNGP05.phx.gbl...
> Does anyone have any thoughts on how to test whether a type is available
> without attempting to create an instance of it?
>
>

Just get the type info by putting the name of the type in []s

PS> [System.Management.Automation.Host.BufferCell]

IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False BufferCell System.ValueType

PS> [Microsoft.Build.BuildEngine.BuildItem]
Unable to find type [Microsoft.Build.BuildEngine.BuildItem]: make sure that
the assembly containing this type is loaded
..
At line:1 char:39
+ [Microsoft.Build.BuildEngine.BuildItem] <<<<
PS>

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Microsoft Corporation
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"Alex K. Angelopoulos [MVP]" <aka@online.mvps.org> wrote in message
news:%23XUOTVMtGHA.1956@TK2MSFTNGP05.phx.gbl...
> Does anyone have any thoughts on how to test whether a type is available
> without attempting to create an instance of it?
>
>

"Jeffrey Snover [MSFT]" <jsnover@microsoft.com> wrote in message
news:uHh3XFPtGHA.2260@TK2MSFTNGP03.phx.gbl...
> Just get the type info by putting the name of the type in []s

.....

> PS> [Microsoft.Build.BuildEngine.BuildItem]
> Unable to find type [Microsoft.Build.BuildEngine.BuildItem]: make sure
> that the assembly containing this type is loaded
> .
> At line:1 char:39
> + [Microsoft.Build.BuildEngine.BuildItem] <<<<
> PS>

I rather like this approach, but I've noticed it can be hard to control the
error output from it. For example, if I want to test for type availability
and work around it myself, I would expect that I could do something like
this:

Invoke-Expression {[Microsoft.Build.BuildEngine.BuildItem]} -ev x -ea
SilentlyContinue

Unfortunately, that doesn't suppress error output or populate $x with the
error results. This is kind of tangential to the problem, but it might be a
nice topic for a blog entry as well - why doesn't this work as I expected,
and what is the best way to capture the error and suppress the error output
when dealing with expressions or script blocks where ErrorVariable and
ErrorAction aren't available?

Interesting. This - or, a little closer, Jacques' variation - can also be
used to enumerate all available types.

Some of the type names returned seem to be bogus, possibly due to oddities
in .NET itself. For example, I get back System.DateTimeFormat as a full name
for a type, and it cannot be created or referenced. However, if I look up
DateTimeFormat in the .NET docs, I get a hit for
System.Globalization.DateTimeFormatInfo, which actually CAN be referenced.

"Jouko Kynsijärvi" <jouko.kynsijarvi@nospam.nospam> wrote in message
news:OWyqDlOtGHA.3912@TK2MSFTNGP03.phx.gbl...
> Alex K. Angelopoulos [MVP] wrote:
>> Does anyone have any thoughts on how to test whether a type is
>> available without attempting to create an instance of it?
>
> This is pretty fast:
>
> function IsTypeLoaded([string]$typeName, [string]$assemblyName) {
> foreach ($asm in [AppDomain]::CurrentDomain.GetAssemblies()) {
> if ($asm.GetName().Name -eq $assemblyName) {
> if ($asm.GetType($typeName) -ne $null) {
> return $true
> }
> }
> }
> return $false
> }
>
> IsTypeLoaded 'System.Data.DataSet' 'System.Data'
>
>

"Alex K. Angelopoulos [MVP]" wrote:
>
> Invoke-Expression {[Microsoft.Build.BuildEngine.BuildItem]} -ev x -ea
> SilentlyContinue
>
> Unfortunately, that doesn't suppress error output or populate $x with the
> error results.

I am not sure why Erroraction preference for the cmdlet was not honored or
not.
So i have set the error action preference in another scope to suppress the
error message and set the error message(returned by "trap" statement) to the
variable named "$err"

==============================
[^_^]PS[38]>& { $ErrorActionPreference = "SilentlyContinue";
[Microsoft.Build.BuildEngine.BuildItem]; trap { $_; } } | Set-Variable err
[^_^]PS[39]>$err
Unable to find type [Microsoft.Build.BuildEngine.BuildItem]: make sure that
the assembly containing this type is loaded
..
At line:1 char:89
+ & { $ErrorActionPreference = "SilentlyContinue";
[Microsoft.Build.BuildEngine.BuildItem]; <<<< trap { $_; } } | Set
-Variable err
==============================

I could have used automatic variable "$error" to check if an error was
generated but with $error, i couldn't tell if the last error is actually an
error generated by the last statement or not since "$?" always returns true
for "& { $ErrorActionPreference = "SilentlyContinue";
[Microsoft.Build.BuildEngine.BuildItem] }" since i am suppressing the error.