Casting a (single) number to System.Collections.IEnumerable inappropriately converts to a (single) string

[mklement0]

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

Note:

• Casting to an interface should never change the operand data type, yet that is what happens here with numeric input types.
• A cast from a type that does not implement IEnumerable should fail, consistently.
• (As an aside, because it may be surprising: casting to [IEnumerable] (or [IEnumerable[char]]) from a string works correctly, given that [string] implements those interfaces, for enumeration of a string's characters)

using namespace System.Collections
using namespace System.Collections.Generic

# With [int] input, for instance.
# !! -> 'System.String'
# Other (non-enumerable) types, e.g. [datetime], cause an error, as expected, and so does use of the
# the generic interface; e.g. 
#    [IEnumerable] (Get-Date)  
#    [IEnumerable[int]] 42
([IEnumerable] 42).GetType().FullName

Expected behavior

The cast should fail, given that [int] doesn't implement IEnumerable.

Actual behavior

'System.String' is output, implying that the cast converted the [int] operand to [string]

Error details

No response

Environment data

PowerShell Core 7.3.1
PowerShell Core 7.4.0-preview.1
(Also WinPS)

Visuals

No response

[237dmitry]

In 7.3.1 (Linux) it returned error

$  [System.Collections.Generic.IEnumerable] 42                             
InvalidOperation: Unable to find type [System.Collections.Generic.IEnumerable].

$  [System.Collections.Generic.IEnumerable[int]] [int[]] 42
42

[mklement0]

You have a typo: [System.Collections.Generic.IEnumerable] 42 -> [System.Collections.IEnumerable] 42; the behavior isn't platform-specific.

[rkeithhill]

The Engine WG reviewed this issue today and agree that it is a bug that needs to be investigated for a potential fix.

[ninmonkey]

Here is a similar error where @( String ) fails to coerce to [string[]] when using a List[String]

# works
[Collections.Generic.List[Object]]$names = 'bob', 'jen'
$names.AddRange(@( 'sue', 'bill'))

# errors
[Collections.Generic.List[String]]$names2 = 'bob', 'jen'
$names2.AddRange(@( 'sue', 'bill'))

Cannot convert argument "collection" with 
     value: "Object[]", 
     for "AddRange" 
     to type "IEnumerable`1[String]": 

"Cannot convert the "Object[]" value 
    of type "Object[]" 
    to type "IEnumerable`1[String]"."

[scriptingstudio]

This works $names2.AddRange([string[]]( 'sue', 'bill'))
You have to use explicit type because you have a typed list

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