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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"A dictionary type that only implements the generic IDictionary interface is unexpectedly enumerated in the pipeline","articleBody":"PowerShell makes a hard-coded exception for types that implement the _non-generic_ `System.Collections.IDictionary` interface with respect to behavior in the pipeline: even though such types are _enumerable_, PowerShell sends them _as a whole_ through the pipeline.\r\n\r\nSource code here: https://github.com/PowerShell/PowerShell/blob/48c7e112db8f0506a74555c83ecb8bec509b6597/src/System.Management.Automation/engine/LanguagePrimitives.cs#L523-L543\r\n\r\nHowever, some types _only_ implement the _generic_ equivalent of this interface, `System.Collections.Generic.IDictionary\u003cTKey, TValue\u003e`.\r\nSuch type are therefore unexpectedly _enumerated_ in the pipeline, i.e their _key-value_ pairs are sent rather than the dictionary itself.\r\n\r\nNote that while with the `IEnumerable` / `IEnumerable\u003cType\u003e` interface pair implementing the generic version _implicitly_ also implements the non-generic one, this does _not_ apply to the `IDictionary` / `IDictionary\u003cTKey, TValue\u003e` pair.\r\n\r\nI don't know what the official recommendations are in this case, but at least one notable example of a type that _only_ implements the generic interface is [`System.Dynamic.ExpandoObject`](https://docs.microsoft.com/en-US/dotnet/api/System.Dynamic.ExpandoObject), used in the repro below.\r\n\r\n## Steps to reproduce\r\n\r\n```powershell\r\n$o = [System.Dynamic.ExpandoObject]::new(); $o.one = 1; $o.two = 2\r\n\r\n($o | Measure-Object).Count | Should -Be 1\r\n```\r\n\r\n## Expected behavior\r\n\r\nThe test should succeed: the `IDictionary`2`-implementing type's instance should be sent _as a whole_ through the pipeline.\r\n\r\n## Actual behavior\r\n\r\nThe test fails, because the instance is enumerated and its key-value pairs are sent through the pipeline.\r\n\r\n```none\r\nInvalidResult: Expected 1, but got 2.\r\n```\r\n\r\n## Environment data\r\n\r\n```none\r\nPowerShell Core 7.2.0-preview.4\r\n```\r\n","author":{"url":"https://github.com/mklement0","@type":"Person","name":"mklement0"},"datePublished":"2021-04-11T19:58:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":21},"url":"https://github.com/15204/PowerShell/issues/15204"}