Update AV1125: Don't expose stateful objects through static members#353
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Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
bkoelman
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Mar 29, 2026
| A stateful object is an object that contains many properties and lots of behavior behind it. If you expose such an object through a static property or method of some other object, it will be very difficult to refactor or unit test a class that relies on such a stateful object. In general, introducing a construct like that is a great example of violating many of the guidelines of this chapter. | ||
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| A classic example of this is the `HttpContext.Current` property, part of ASP.NET. Many see the `HttpContext` class as a source of a lot of ugly code. | ||
| A classic example of this is the `HttpContext.Current` property, part of classic ASP.NET. Many see this as a source of a lot of ugly code, because it hides an implicit dependency on a global state object. Instead, make dependencies explicit by injecting them through a constructor or method parameter. |
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We don't need to refer to classic ASP.NET; there are plenty of cases in modern .NET that are still a pain when writing tests:
System.Environment.MachineNameSystem.Environment.GetEnvironmentVariable(can't run tests in parallel that depend on it)System.DateTime.UtcNowSystem.IO.Path.Combine(depends on OS-level directory separator)System.IO.Path.GetInvalidFileNameCharsSystem.IO.File.Exists
The rule title could be changed to:
Don't expose global state through static members
- Rename title to 'Don't expose global state through static members' - Replace classic ASP.NET example with modern .NET examples (Environment.MachineName, DateTime.UtcNow, File.Exists, etc.) - Note testability issues, especially parallel test execution - Suggest TimeProvider as a modern abstraction over DateTime.UtcNow Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
- Broaden title to 'Don't hide dependencies behind static members' to cover both global state and environmental dependencies - Clarify the closing sentence to emphasize injection of an abstraction rather than vague 'well-known abstractions' Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Updates guideline AV1125 to focus on avoiding static members that expose global/environment-dependent state, using concrete .NET examples and steering readers toward dependency injection/abstractions for testability.
Changes:
- Renames the guideline title to emphasize “global state” rather than “stateful objects”.
- Replaces the previous paragraph with examples of problematic static/global dependencies and a short rationale.
- Adds a recommendation to inject or abstract these dependencies (e.g.,
TimeProvider).
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| title: Don't hide dependencies behind static members | ||
| severity: 2 | ||
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| A stateful object is an object that contains many properties and lots of behavior behind it. If you expose such an object through a static property or method of some other object, it will be very difficult to refactor or unit test a class that relies on such a stateful object. In general, introducing a construct like that is a great example of violating many of the guidelines of this chapter. | ||
| A well-known example is `HttpContext.Current` from classic ASP.NET. But modern .NET still has plenty of cases where static members expose global or environment-dependent state, such as `Environment.MachineName`, `DateTime.UtcNow`, `Environment.GetEnvironmentVariable`, and `File.Exists`. These are problematic because: |
| - They make unit testing difficult, especially running tests in parallel. | ||
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| A classic example of this is the `HttpContext.Current` property, part of ASP.NET. Many see the `HttpContext` class as a source of a lot of ugly code. | ||
| Instead, make dependencies explicit by injecting them through a constructor or method parameter, or by injecting an abstraction (e.g., `TimeProvider` instead of calling `DateTime.UtcNow` directly). |
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* Make sure the site works properly with Ruby 3.1 * Add AV0100: Understand the boundaries of your codebase (#300) * Add AV0105: Use design patterns to communicate intent (#301) * Add AV0110: Prefer composition over class inheritance (#302) * Add AV0110 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/0110.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Add AV0112: Apply the Principle of Least Surprise (#303) * Add AV0115 guideline (#304) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV0120: You Ain't Gonna Need It (YAGNI) (#305) * Add AV0120 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/0120.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Update _rules/0120.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Update _rules/0120.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Add AV0125: Don't Repeat Yourself (DRY) within boundaries (#306) * Update explanation of code boundaries and coupling Clarified the reasoning for preventing unnecessary coupling between components. * Add AV0135 guideline (#308) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1582 guideline (#318) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1608 guideline (#323) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1610 guideline (#324) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1708 guideline (#372) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1562 guideline (#368) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1800 guideline (#375) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1521 guideline (#361) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1520 guideline (#360) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1140 guideline (#356) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Remove AV1530: Don't change a loop variable inside a `for` loop or a collection in a `foreach` loop (#363) * Update AV1530 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Address review comments on AV1530: update title and add foreach collection example Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com> Agent-Logs-Url: https://github.com/dennisdoomen/CSharpGuidelines/sessions/983488b6-53b6-4360-876c-4576219b2d4f * Remove AV1530 rule file entirely Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com> Agent-Logs-Url: https://github.com/dennisdoomen/CSharpGuidelines/sessions/0ce85de6-5278-491a-87c7-607ef017b67b --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com> * Update AV1250 guideline (#358) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1115 guideline (#352) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1025 guideline (#351) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1020 guideline (#350) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1011 guideline (#348) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1010 guideline (#347) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1003 guideline (#345) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1618 guideline (#326) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1615: Prefer inline literals over constant variables in tests (#325) * Add AV1615 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/1615.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Update AV1835 guideline (#378) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1825 guideline (#377) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update AV1000: A class or interface should have a single purpose (#344) * Update AV1000 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/1000.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Remove AV2235 guideline (#342) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1602: Postfix test classes with `Specs` instead of `Tests` (#321) * Add AV1602 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Rename nested class Order_placement to OrderPlacement Renamed nested class for better readability. --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add AV1605: Test behavior, not implementation details (#322) * Add AV1605 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/1605.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Add General Guidelines page (#385) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Add Testability Guidelines page (#386) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update Links & Articles page (#387) * Update C ov er An dS ty le s page (#384) * Update AV2400 guideline (#382) * Split minor site updates from PR 298 (#383) * Add AV1600 guideline (#320) * Add AV1578 guideline (#317) * Update AV1706: Don't use abbreviations (#371) * Update AV1701 guideline (#370) * Update AV1755: Only use `Async` or `TaskAsync` as a suffix when a method has both synchronous and asynchronous versions (#374) * Clarify suffix usage for Async methods (#393) Follow-up for #374, to align with the replacement of "version" with "variant". * Update AV2305: Document all `public`, `protected` and `internal` types and members (#381) * Update AV2202: Prefer language syntax over explicit calls to underlying implementations (#379) * Update AV1820: Only use `async` for I/O-bound or long-running activities (#376) * Remove AV1580 guideline (#392) * AV0125: Consider duplicating simple logic across modules to reduce coupling (#369) * Update AV1554 guideline (#367) * Update AV1553 guideline (#366) * Update AV1546 guideline (#365) * Update AV1545: Don't use an `if`-`else` construct instead of a simple (conditional) assignment (#364) * Update AV1523 guideline (#362) * Update AV1500: Methods should not exceed 15 statements (#359) * Remove AV1230 guideline (#357) * Update AV1137: Keep parameters as specific and narrow as possible (#355) * Update AV1130: Return interfaces to unchangeable collections (#354) * Update AV1125: Don't expose stateful objects through static members (#353) * Update AV1013: Don't cast a base class to one of its derived classes (#349) * Add LSP example with polymorphism to AV1011 (#396) * Update AV1004: Use an interface rather than a base class to support multiple implementations (#346) * Remove AV2307 guideline (#343) * Remove AV2221 guideline (#341) * Remove AV2201 guideline (#339) * Remove AV1738 guideline (#338) Split from #298. Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Remove AV1737 guideline (#337) * Remove AV1568 guideline (#336) * Remove AV1532: Avoid nested loops (#334) * Remove AV1525 guideline (#333) * Remove AV1510 guideline (#332) * Remove AV1220 guideline (#331) * Add AV2308: Document what a member tries to do, not what it does or how it does it (#330) * Add AV2225: Use deconstruction to simplify variable assignments (#329) * Add AV1622: Test concrete implementations as part of a larger integration scope (#328) * Add AV1622 guideline Split from #298. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Update _rules/1622.md Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> * Add AV1620: Test reusable components separately from their consumers (#327) * Add AV1585: Make properties required when they must be set during initialization (#319) * Add AV1155: Use the `field` keyword in auto-properties when additional logic is needed (#316) * Add AV1150: Avoid local functions (#315) * Add AV1145: Use extension members to add behavior without modifying the original type (#314) * Add AV1035: Use primary constructors when they improve readability (#313) * Add AV1032: Consider a delegate instead of an interface with a single method (#312) * Add AV1030: Know when to use a record and when to use a class (#311) * Add AV1002: Only pass things to a constructor that most or all members need (#309) * Remove AV2207 guideline (#340) * Add AV0130: Apply the three pillars of object-oriented programming (#307) * Fix c# fencing to use csharp in assertion-comparison.html Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Remove severity field from all rules The severity rating is no longer used. This removes: - The severity front matter field from all 130 rule files - The severity icon <img> from the rule-category layout - The unused severity images (1.png, 2.png, 3.png) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Bart Koelman <10324372+bkoelman@users.noreply.github.com> Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com>
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This PR updates guideline AV1125.
It was split out of #298 so the change can be reviewed independently.
Files:
Part of the replacement for #298.