Types tagged with ImmutableAttribute must be immutable

Rule ND1909 Immutability

A type is immutable if its instance fields are only assigned inline or from constructor(s). NDepend.Attributes.ImmutableAttribute (from NDepend.API.dll, or your own attribute, adapting the rule) expresses in code that a type is immutable; this rule continuously checks it and warns when a tagged type is no longer immutable.

How to fix

Find which modification broke immutability (the culpritFields list helps), then refactor the type back to immutability.

Estimated Debt: 5 minutes plus 10 minutes per culprit field.

CQLinq source

This rule is written in CQLinq, C# LINQ over the NDepend code model. It ships with every new NDepend project: you can read it, adapt it, or use it as a starting point for your own custom rules.

// <Name>Types tagged with ImmutableAttribute must be immutable</Name>
// <Id>ND1909:TypesTaggedWithImmutableAttributeMustBeImmutable</Id>

warnif count > 0 
from t in Application.Types where 
   t.HasAttribute ("NDepend.Attributes.ImmutableAttribute".AllowNoMatch()) && 
  !t.IsImmutable
let culpritFields = t.Fields.Where(f => !f.IsStatic && !f.IsImmutable)
select new { 
   t, 
   culpritFields,
   Debt = (5+10*culpritFields.Count()).ToMinutes().ToDebt(),
   Severity = Severity.High
}

//<Expl>
// The *{0}* is tagged with the *ImmutableAttribute* yet it is mutable:
// its *{1}* can be assigned.
// This attribute indicates a commitment to keep this type immutable
// so make sure its instance states cannot be changed after construction.
//</Expl>

//<Desc>
// A type is immutable if its instance fields are only assigned inline or
// from constructor(s). **NDepend.Attributes.ImmutableAttribute** (from
// *NDepend.API.dll*, or your own attribute, adapting the rule) expresses in
// code that a type is immutable; this rule continuously checks it and warns
// when a tagged type is no longer immutable.
//</Desc>

//<HowToFix>
// Find which modification broke immutability (the *culpritFields* list
// helps), then refactor the type back to immutability.
//
// Estimated Debt: 5 minutes plus 10 minutes per culprit field.
//</HowToFix>

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