René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Can we allow script-block parameter values (delay-bind script blocks) for non-pipeline-binding parameters too?","articleBody":"Being able to pass script blocks ad hoc in order to calculate per-input-object parameter values is a [great general-purpose feature](https://github.com/PowerShell/PowerShell-Docs/issues/2338).\r\n\r\nHowever, it is currently _limited to parameters that are explicitly defined as pipeline-binding_.\r\n\r\nA widely used application of this technique is with `Rename-Item`'s `-NewName` parameter, where a script block is passed to calculate the new name; e.g.:\r\n\r\n```powershell\r\n# Rename all *.rtf files to *.txt files\r\nGet-Item *.rtf | Rename-Item -NewName {  $_.BaseName + '.txt' } -WhatIf\r\n```\r\n\r\nHowever, the above _only_ works because `-NewName` too is defined as pipeline-binding (`ValueFromPipelineByPropertyName`, in this case).\r\n\r\nThe ability to pass a script block to _any_ parameter (other than those typed `[object]` or `[scriptblock]`) of a command that accepts pipeline input in principle - whether or not that parameter is itself pipeline-binding - would make this technique useful in a much wider array of situations.\r\n\r\nIs there a conceptual barrier to removing this restriction (overall, the cmdlet/advanced function would still have to have at least _one_ pipeline-binding parameter)?\r\n\r\nTechnically, this would be a breaking change, albeit hopefully one that falls into [Bucket 3: Unlikely Grey Area](https://github.com/PowerShell/PowerShell/blob/master/docs/dev-process/breaking-change-contract.md#bucket-3-unlikely-grey-area):\r\n\r\nWhat happens currently if you try to pass a script block to a differently typed non-pipeline-binding parameters is that an attempt is made to convert the script block to the parameter's type (unless the parameter is `[object]` or `[scriptblock]`, which would continue to be exempt). \r\nThis fails with most types, but in the case of a `[string]` parameter you currently do get the script block's _contents_ as a string value.  \r\nArguably, though, users who expect script blocks type their parameters a such.\r\n\r\n\r\n\r\n------------------\r\n\r\nHere's an example with an advanced function:\r\n\r\n```powershell\r\nfunction Rename-Foo {\r\n    [CmdletBinding()]\r\n    param(\r\n        [Parameter(Mandatory, ValueFromPipeline)]\r\n        [System.IO.FileSystemInfo] $InputObject\r\n        ,\r\n        # WISHFUL THINKING: The `ValueFromPipelineByPropertyName` shouldn't be necessary.\r\n        [Parameter(Mandatory, ValueFromPipelineByPropertyName)]\r\n        [string] $NewName\r\n    )\r\n\r\n    process {\r\n        \"Will rename $($InputObject.Name) to $NewName.\"\r\n    }\r\n\r\n}\r\n\r\nPS\u003e Get-Item foo.txt, bar.txt | Rename-Foo -NewName { $_.Name + '!!' }\r\nWill rename foo.txt to foo.txt!!\r\nWill rename bar.txt to bar.txt!!\r\n```\r\n\r\n\r\nEnvironment data\r\n----------------\r\n\r\nWritten as of:\r\n\r\n```powershell\r\nPowerShell Core v6.0.2\r\n```\r\n","author":{"url":"https://github.com/mklement0","@type":"Person","name":"mklement0"},"datePublished":"2018-05-08T13:19:23.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":29},"url":"https://github.com/6837/PowerShell/issues/6837"}