How to suppress overflow-checking in PowerShell?

问题

PowerShell seems to perform bounds-checking after arithmetic operations and conversions. For instance, the following operations fail:

[byte]$a = 255
$a++

$a = [byte]256

Is there any way to enforce overflows or the typecast without resorting to a manual calculation via modulo or C# and Add-Type?

回答1:

The behavior you want in PowerShell is achievable, though, it's a bit of a hack; and maybe there's a better way.

If you just want cryptographic functionality though, it's worth calling out, that there's a TON of that already built-in to the BCL, and it's fully accessible from PowerShell (MD5, SHA, RSA, X509, a ton of other stuff too).

But if you're dead set on performing unchecked arithmetic in PowerShell, this is a hack that should give you what you want (basically we're embedding C# code, and using the unchecked keyword):

$members = @' 
public static UInt32 ToUInt32(int value)
{
    unchecked
    {
        return (UInt32)value;
    }
}


public static byte ToByte(int value)
{
    unchecked
    {
        return (byte)value;
    }
}
'@;

$type = Add-Type -Name "Convert" -Namespace "Helpers" `
        -MemberDefinition $members -PassThru -ErrorAction SilentlyContinue;

Usage:

PS C:\Some\Folder> [Helpers.Convert]::ToUInt32(-1);
4294967295

PS C:\Some\Folder> [Helpers.Convert]::ToByte(-1);
255

PS C:\Some\Folder> [Helpers.Convert]::ToByte(256);
0

Of Note:

• We're calling [Helpers.Convert]::To... and not [System.Convert]::To....
• If you need other methods, the actual C# methods will need to be inserted into the $members block at the top of the code.
• If you run Add-Type multiple times in a row for the same Namespace and Name combination, in the same PowerShell session, it will fail; and you will be left with the previously registered type. -- I've added -ErrorAction SilentlyContinue to ignore this specific scenario. -- That way, you can dump this code into a .ps1 script, and call it every single time, before you use them methods, and they will always be present. -- But if you are modifying the C# code and retesting, you will want to change the type name after every change you make; it's kind of painful.

回答2:

PowerShell is a scripting language, not a programming language, it doesn't support a lot of advanced techniques like overloading operators (which would be handy in this case).

To add to the things you have already suggested, you could just catch the error.

[byte]$a = 255
try {$a++} catch {$a=1}

Or write your own function and do some modulo fun in there.

来源：https://stackoverflow.com/questions/15720138/how-to-suppress-overflow-checking-in-powershell