remove this useless assignment to local variable c#

Remove this useless assignment to variable

I am using SimpleDataTables JS Library and their minimal suggested implementation: const dataTable = new DataTable("#myTable");

In SC this throws me an Remove this useless assignment to variable "dataTable". and an Remove the declaration of the unused 'dataTable' variable.

If I remove the assignement SC tells me to Either remove this useless object instantiation of "DataTable" or use it.

In SC, the FIRST approach is considered a code-smell, the second approach is considered a bug. So I prefer to use first approach, but still SC is not fully happy.

With my rather limited knowledge of JS, I would say simply doing new DataTable("#myTable"); is the right approach. Of course, strictly speaking, that library should probably not have sideffects when instantiating the object but rather provide a method (like DataTable->run()), but that is not the case.

Is there some other approach to do it “correctly” other than marking this as a false alarm?

Indeed you are using some lib probably having side-effects on constructor execution. I don’t think we will support this lib (I see from npm downloads it’s not very popular), so it’s up to you to ignore the issues.

I would keep the variable (it seems the recommended way as you might hook some events on it later). So either you could “won’t fix” the issues, or you can set in SC settings to ignore particular files for these rules (Administration → General Settings → Analysis Scope → Ignore Issues on Multiple Criteria).

Understood, I will maybe switch to the official data tables lib by jQuery. I had chosen the current one because it is much lighter, but in the end with modern computers and servers etc this doesn’t matter that much anyway.

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Useless assignment to local variable ¶

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A value is assigned to a local variable, but either that variable is never read later on, or its value is always overwritten before being read. This means that the original assignment has no effect, and could indicate a logic error or incomplete code.

Recommendation ¶

Ensure that you check the program logic carefully. If a value is really not needed, consider omitting the assignment. Be careful, though: if the right-hand side has a side effect (like performing a method call), it is important to keep this to preserve the overall behavior.

The following example shows six different types of assignments to local variables whose value is not read:

In ParseInt , the result of the call to int.TryParse is assigned directly to the unread local variable success .

In IsDouble , the out argument of the call to int.TryParse is assigned to the unread local variable i .

In ParseDouble , the exception thrown by the call to double.Parse in case of parse failure is assigned to the unread local variable e .

In Count , the elements of ss are assigned to the unread local foreach variable s .

In IsInt , o is assigned (in case o is an integer) to the unread local type test variable i .

In IsString , o is assigned (in case o is a string) to the unread local type case variable s .

The revised example eliminates the unread assignments.

References ¶

Wikipedia: Dead store .

MSDN, Code Analysis for Managed Code, CA1804: Remove unused locals .

Microsoft: What’s new in C# 7 - Discards .

Common Weakness Enumeration: CWE-563 .

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How to resolve C# error: Use of unassigned local variable

The "Use of unassigned local variable" error occurs when you try to use a local variable before assigning a value to it. In C#, local variables are not automatically initialized and must be assigned a value before they can be used. To resolve this error, follow these steps:

• Initialize the variable when declaring it:

Assign an initial value to the variable when you declare it:

• Assign a value to the variable before using it:

Ensure that you assign a value to the variable in every possible code path before using it:

• Use a default value if the variable may not be assigned in some code paths:

If your code logic allows the variable to be unassigned in some scenarios, use a default value:

By ensuring that all local variables are assigned a value before they are used, you can resolve the "Use of unassigned local variable" error in your C# code.

C# Use of Unassigned Local Variable Error:

• Occurs when trying to use a variable that hasn't been assigned a value.
• Example code: int number; Console.WriteLine(number); // Error: Use of unassigned local variable 'number'

Resolving Unassigned Variable Error in C#:

• Assign a value to the variable before using it.
• Example code: int number = 42; Console.WriteLine(number); // No error

Avoiding Unassigned Variable Issues in C#:

• Initialize variables with default values if needed.
• Example code: int number = 0; // Default value

Handling Null or Default Values in C# Variables:

• Use nullable types or default values to handle potential null values.
• Example code: int? nullableNumber = null; // Nullable type int defaultValue = default; // Default value

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Sonar "useless assignment to local variable" workaround?

I am working towards improving my code, and I came across this issue from Sonar:

Fact is, it is not useless, as I am using it just after in the code:

Sonar still tells me that "uiRequest" is useless, why ? It is not, as I don't want it to reach the code if it is null. I tried initializing it ( uiRequest = new UiRequest() ) but it keeps telling me that it is useless.

Anyone got an idea about why Sonar behaves like this / how to correct this ?

• sonar-runner

• 4 It is absolutely useless because the block of code that uses it callService(uiRequest, vauban) would never be reached if uiRequest were using the assignment to null. –  rmlan Commented May 22, 2017 at 14:10
• 1 not uiRequest is useless, but assigning null to it. –  Abacus Commented May 22, 2017 at 15:41

4 Answers 4

Your issue simplifies to:

There are two potential paths through this code:

• a() returns true . x is assigned b() then c(x) is called.
• a() returns false . An exception is thrown and c(x) is not called.

Neither of these paths calls c(x) using the initial assignment of null . So whatever you assigned at first, is redundant.

Note that this would also be an issue if the initial assignment was something other than null. Unless the right-hand-side of the assignment has a side effect , any assignment is wasted. (Sonar analyses for side-effects)

This is suspicious to Sonar:

• Maybe the programmer expected the first assignment to have an effect -- it doesn't, so perhaps it's a bug.
• It's also about code clarity -- a future human reader of the code might waste time wondering what the initial value is for.
• If the right-hand-side had involved computation, but had no side effect, it would be wasted computation.

You can fix this in two ways:

Firstly just removing the = null , leaving Foo x; - Java is clever enough to realise that all routes to c(x) involve an assignment, so this will still compile.

Better yet, move c(x) into the block:

This is logically equivalent, neater, and reduces the scope of x . Reducing scope is a good thing. Of course, if you need x in the wider scope, you can't do this.

One more variation, also logically equivalent:

... which responds well to "extract-method" and "inline" refactorings:

Use whichever communicates your intent best.

You can avoid the warning and perhaps have slightly more readable code by:

What about moving it into the if statement?

Or throw exception in the if statement and just have no else clause. i.e let the normal case be the "happy path".

The assignment is useless because no code can possibly see that assigned value.

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Remove unnecessary expression value (IDE0058)

• 4 contributors

This rule flags unused expression values. For example:

You can take one of the following actions to fix this violation:

If the expression has no side effects, remove the entire statement. This improves performance by avoiding unnecessary computation.

If the expression has side effects, replace the left side of the assignment with a discard (C# only) or a local variable that's never used. This improves code clarity by explicitly showing the intent to discard an unused value.

The options for this specify whether to prefer the use of a discard or an unused local variable:

• C# - csharp_style_unused_value_expression_statement_preference
• Visual Basic - visual_basic_style_unused_value_expression_statement_preference

For information about configuring options, see Option format .

csharp_style_unused_value_expression_statement_preference

visual_basic_style_unused_value_expression_statement_preference

Suppress a warning

If you want to suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

To disable the rule for a file, folder, or project, set its severity to none in the configuration file .

To disable all of the code-style rules, set the severity for the category Style to none in the configuration file .

For more information, see How to suppress code analysis warnings .

• Remove unnecessary value assignment (IDE0059)
• Code style rules reference

Additional resources

Solving Sonar's 'Remove Useless Assignment of Local Variable' Error in Swift

Abstract: Learn how to resolve SonarQube's 'Remove Useless Assignment of Local Variable' error in Swift by understanding its cause and using different workarounds.

Solving Sonar's "Remove Useless Assignment to Local Variable" Error in Swift

Sonar is a popular tool used for code analysis and review. It helps developers identify and fix issues in their code, making it more readable, maintainable, and secure. One common issue that Sonar flags is the "Remove Useless Assignment to Local Variable" error in Swift. This error occurs when a local variable is assigned a value that is not used in the code. In this article, we will discuss how to solve this error in Swift.

Understanding the Error

To understand the error, let's consider an example:

In this example, we declare two local variables, x and y. We assign the value 5 to x and then calculate the value of y by multiplying x by 2. However, we never use the value of x again in the code. Therefore, Sonar flags the assignment of x as a useless assignment.

Solving the Error

To solve the error, we need to ensure that every local variable is used in the code. We can do this by either using the variable or removing its declaration. In the above example, we can remove the declaration of x, as it is not used in the code:

Alternatively, we can use the value of x in the code:

In this example, we print the value of x to the console, ensuring that it is used in the code.

Using Sonar to Identify Useless Assignments

Sonar can help us identify useless assignments in our code. To do this, we need to configure Sonar to analyze our Swift code. We can do this by installing the SonarSwift plugin and configuring it to analyze our project. Once we have done this, Sonar will flag any useless assignments in our code, allowing us to fix them.

The "Remove Useless Assignment to Local Variable" error in Swift is a common issue that Sonar flags. To solve this error, we need to ensure that every local variable is used in the code. We can do this by either using the variable or removing its declaration. Sonar can help us identify useless assignments in our code, allowing us to fix them and improve the quality of our code.

Remove Useless Assignment to Local Variable

Supported Languages

Tags: :  Swift SonarQube Software Development

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Rubocopエラー「Useless assignment to variable」の解決例

上記エラーを調べると、「使っていないローカル変数の定義がある」というエラーのようで 削除すれば解決するとの事でした。

しかし、今回はちゃんと使っている内容で、書き方の問題のようでした。 以下のように、if文などの後に 明示的に使用している記載が必要 とのことでした。

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