Methods tagged with PureAttribute must be pure

Rule ND1911 Immutability

How to fix

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>Methods tagged with PureAttribute must be pure</Name>
// <Id>ND1911:MethodsTaggedWithPureAttributeMustBePure</Id>

warnif count > 0 
from m in Application.Methods where 
  ( m.HasAttribute ("NDepend.Attributes.PureAttribute".AllowNoMatch()) || 
    m.HasAttribute ("System.Diagnostics.Contracts.PureAttribute".AllowNoMatch()) ) &&
  ( m.ChangesObjectState || m.ChangesTypeState ) &&
    m.NbLinesOfCode > 0

let fieldsAssigned = m.FieldsAssigned

select new { 
   m, 
   m.NbLinesOfCode, 
   fieldsAssigned,
   Debt = 15.ToMinutes().ToDebt(),
   Severity = Severity.High
}

//<Expl>
// The *{0}* is tagged with the *PureAttribute* yet it assigns the *{2}*.
// This attribute indicates a commitment to keep this method pure
// so make sure it doesn't change any state at runtime.
//</Expl>

//<Desc>
// A pure method changes no instance or static field: a **function**
// producing a result from inputs, simplifying code by **limiting
// side-effects**. A **PureAttribute** expresses purity in code; this rule
// continuously checks it and warns when a tagged method is no longer pure.
//
// Use *NDepend.Attributes.PureAttribute* (from *NDepend.API.dll*),
// *System.Diagnostics.Contracts.PureAttribute* (honored by the compiler
// only with Microsoft Code Contract enabled), or your own *PureAttribute*
// (adapting the rule).
//</Desc>

//<HowToFix>
// Find which modification broke the method purity, then refactor it back
// to purity.
//</HowToFix>

Open in the interactive Rules Explorer · All default rules

Immutability: all 15 items

• Fields should be marked as ReadOnly when possible ND1900
• Avoid non-readonly static fields ND1901
• Avoid static fields with a mutable field type ND1902
• Structures should be immutable ND1903
• Immutable struct should be declared as readonly ND1914
• Property Getters should be pure ND1904
• A field must not be assigned from outside its parent hierarchy types ND1905
• Don't assign a field from many methods ND1906
• Do not declare read only fields with mutable reference types ND1907
• Public read only array fields can be modified ND1908
• Types tagged with ImmutableAttribute must be immutable ND1909
• Types immutable should be tagged with ImmutableAttribute ND1910
• Methods tagged with PureAttribute must be pure ND1911
• Pure methods should be tagged with PureAttribute ND1912
• Record should be immutable ND1913