René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Improve mutable struct detection","articleBody":"# Summary of the new feature/enhancement\r\n\r\nWhen assigning a struct to a variable, some checks are done to determine if the struct is mutable.  The current code path checks if there are:\r\n\r\n1. Any public instance fields\r\n1. Any public instance properties with a set accessor\r\n1. Any public instance methods\r\n\r\nThis can be simplified by checking if the struct is decorated with the `IsReadOnlyAttribute`.  This would allow PS to assume any struct that wasn't declared explicitly as read only with the C# `readonly` modifier ([SharpLab example](https://sharplab.io/#v2:D4AQzABATgpghgEwPYDsA2BPCBnALlAVwGNcIBZDAZX2NIG8BfIA)) to be mutable.  This would also probably result in *less* false positives because most structs have a public field (even if `initonly`) or a public method, even these explicitly `readonly` structs.\r\n\r\n# Proposed technical implementation details (optional)\r\n\r\nThis method:\r\n\r\nhttps://github.com/PowerShell/PowerShell/blob/947bddfe0474429672745b939d0ec511392e5879/src/System.Management.Automation/engine/runtime/Binding/Binders.cs#L2030-L2063\r\n\r\nShould be changed like this:\r\n\r\n```diff\r\ndiff --git a/src/System.Management.Automation/engine/runtime/Binding/Binders.cs b/src/System.Management.Automation/engine/runtime/Binding/Binders.cs\r\nindex b54fbdfd5..7a0254ccb 100644\r\n--- a/src/System.Management.Automation/engine/runtime/Binding/Binders.cs\r\n+++ b/src/System.Management.Automation/engine/runtime/Binding/Binders.cs\r\n@@ -2034,32 +2034,7 @@ namespace System.Management.Automation.Language\r\n                 return false;\r\n             }\r\n \r\n-            // If there are any fields, the type is mutable.\r\n-            if (type.GetFields(BindingFlags.Public | BindingFlags.Instance).Any())\r\n-            {\r\n-                return true;\r\n-            }\r\n-\r\n-            // If there are any properties with setters, the type is mutable.\r\n-            var properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);\r\n-            for (int index = 0; index \u003c properties.Length; index++)\r\n-            {\r\n-                var property = properties[index];\r\n-                if (property.CanWrite)\r\n-                {\r\n-                    return true;\r\n-                }\r\n-            }\r\n-\r\n-            // If there are any methods other than the property getters, the type might\r\n-            // be mutable, so assume the type is mutable.\r\n-            var methods = type.GetMethods(BindingFlags.Public | BindingFlags.Instance);\r\n-            if (methods.Length != properties.Length)\r\n-            {\r\n-                return true;\r\n-            }\r\n-\r\n-            return false;\r\n+            return !type.IsDefined\u003cSystem.Runtime.CompilerServices.IsReadOnlyAttribute\u003e();\r\n         }\r\n \r\n         private static readonly ConcurrentDictionary\u003cType, bool\u003e s_mutableValueTypesWithInstanceMembers =\r\n```\r\n\r\nRelated issue #12411\r\n\r\n/cc @mklement0 ","author":{"url":"https://github.com/SeeminglyScience","@type":"Person","name":"SeeminglyScience"},"datePublished":"2020-04-22T18:22:29.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":19},"url":"https://github.com/12430/PowerShell/issues/12430"}