CODEWITHSUNDEEP
powershell
lit
lit

Reputation: 16236

Mistake with array raises questions

I made a mistake. I used a FULL STOP between array values rather than a COMMA. What is $x? It appears to be $null. What does this expression mean? Why no error message?

PS 18:48  C:\src\t
>$x = 1.2.3
PS 18:48  C:\src\t
>$x
PS 18:48  C:\src\t
>$x.GetType()
You cannot call a method on a null-valued expression.
At line:1 char:1
+ $x.GetType()
+ ~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

PS 18:48  C:\src\t
>$null -eq $x
True
PS 18:48  C:\src\t
>$x.Count
0

Upvotes: 2

Views: 66

Answers (2)

mklement0
mklement0

Reputation: 437638

To complement Paul G's helpful answer, which explains that the .3 in 1.2.3 is interpreted as accessing a property named 3 on the [double] value that 1.2 is parsed as:

Why no error message?

By default, PowerShell ignores attempts to access non-existent properties on an object and returns $null.

If you use Set-StrictMode -Version 2 or higher, however, a statement-terminating error occurs:

PS> Set-StrictMode -Version 2; 1.2.3
The property '3' cannot be found on this object. Verify that the property exists.
...

See the Set-StrictMode help topic for more information.

While Set-StrictMode is useful for preventing errors such as misspelled variable and property names, it has notable pitfalls:

  • Set-StrictMode is dynamically rather than lexically scoped, which means that all code invoked from a scope in which it is in effect is also affected - and such code may not have been designed for that and therefore break; providing a lexically scoped strict mode to remedy that is the subject of this RFC.

  • with Set-StrictMode -Version 2 or higher, the implicitly added .Count property that unifies PowerShell's handling of scalars and collections is then not available - this should be considered a bug, and has been reported in GitHub issue #2798.

Upvotes: 3

Paul G
Paul G

Reputation: 1229

1.2 is implied as an double type. the second "." tries to invoke a member (either property or method) from the double, since there is no member of an double named "3", $x becomes $null.

Upvotes: 3

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