From f2a497ba0fd1db44286f8fb3301929b69451a0f2 Mon Sep 17 00:00:00 2001 From: Youssef1313 Date: Tue, 20 Dec 2022 20:30:29 +0200 Subject: [PATCH 1/4] Document CA1858: Use StartsWith instead of IndexOf --- .../code-analysis/quality-rules/ca1858.md | 96 +++++++++++++++++++ .../code-analysis/quality-rules/index.md | 1 + .../quality-rules/performance-warnings.md | 1 + docs/fundamentals/toc.yml | 2 + 4 files changed, 100 insertions(+) create mode 100644 docs/fundamentals/code-analysis/quality-rules/ca1858.md diff --git a/docs/fundamentals/code-analysis/quality-rules/ca1858.md b/docs/fundamentals/code-analysis/quality-rules/ca1858.md new file mode 100644 index 0000000000000..8c52497c8a520 --- /dev/null +++ b/docs/fundamentals/code-analysis/quality-rules/ca1858.md @@ -0,0 +1,96 @@ +--- +title: "CA1858: Use StartsWith instead of IndexOf" +description: "Learn about code analyzer rule CA1858 - Use StartsWith instead of IndexOf" +ms.date: 12/20/2022 +ms.topic: reference +f1_keywords: +- CA1858 +- UseStartsWithInsteadOfIndexOfComparisonWithZero +helpviewer_keywords: +- CA1858 +dev_langs: +- CSharp +- VB +--- + +# CA1858: Use StartsWith instead of IndexOf + +| | Value | +| ----------------------------------- | -------------------------------------- | +| **Rule ID** | CA1858 | +| **Category** | [Performance](performance-warnings.md) | +| **Fix is breaking or non-breaking** | Non-breaking | + +## Cause + + is called and its result is compared against zero. + +## Rule description + +It's more efficient and clearer to call than to call and compare the result with zero to determine whether a string starts with a given prefix.. + +## How to fix violations + +Replace the call to with a call to . + +## Example + +The following code snippet shows a violation of CA1855: + +```csharp +bool M(string s) +{ + return s.IndexOf("abc") == 0; +} +``` + +```vb +Function M(s As String) As Boolean + Return s.IndexOf("abc") = 0 +End Function +``` + +The following code snippet fixes the violation: + +```csharp +bool M(string s) +{ + return s.StartsWith("abc"); +} +``` + +```vb +Function M(s As String) As Boolean + Return s.StartsWith("abc") +End Function +``` + +## When to suppress warnings + +It's safe to suppress this warning if performance isn't a concern. + +## Suppress a warning + +If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule. + +```csharp +#pragma warning disable CA1858 +// The code that's violating the rule is on this line. +#pragma warning restore CA1858 +``` + +To disable the rule for a file, folder, or project, set its severity to `none` in the [configuration file](../configuration-files.md). + +```ini +[*.{cs,vb}] +dotnet_diagnostic.CA1858.severity = none +``` + +To disable this entire category of rules, set the severity for the category to `none` in the [configuration file](../configuration-files.md). + +```ini +[*.{cs,vb}] +dotnet_analyzer_diagnostic.category-Performance.severity = none +``` + +For more information, see [How to suppress code analysis warnings](../suppress-warnings.md). diff --git a/docs/fundamentals/code-analysis/quality-rules/index.md b/docs/fundamentals/code-analysis/quality-rules/index.md index 17698d1272324..948544084ab0c 100644 --- a/docs/fundamentals/code-analysis/quality-rules/index.md +++ b/docs/fundamentals/code-analysis/quality-rules/index.md @@ -151,6 +151,7 @@ The following table lists code quality analysis rules. > | [CA1853: Unnecessary call to 'Dictionary.ContainsKey(key)'](ca1853.md) | There's no need to guard `Dictionary.Remove(key)` with `Dictionary.ContainsKey(key)`. already checks whether the key exists and doesn't throw if it doesn't exist. | > | [CA1854: Prefer the 'IDictionary.TryGetValue(TKey, out TValue)' method](ca1854.md) | Prefer 'TryGetValue' over a Dictionary indexer access guarded by a 'ContainsKey' check. 'ContainsKey' and the indexer both look up the key, so using 'TryGetValue' avoids the extra lookup. | > | [CA1855: Use Span\.Clear() instead of Span\.Fill()](ca1855.md) | It's more efficient to call than to call to fill the elements of the span with a default value. | +> | [CA1858: Use StartsWith instead of IndexOf](ca1855.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | > | [CA2000: Dispose objects before losing scope](ca2000.md) | Because an exceptional event might occur that will prevent the finalizer of an object from running, the object should be explicitly disposed before all references to it are out of scope. | > | [CA2002: Do not lock on objects with weak identity](ca2002.md) |An object is said to have a weak identity when it can be directly accessed across application domain boundaries. A thread that tries to acquire a lock on an object that has a weak identity can be blocked by a second thread in a different application domain that has a lock on the same object. | > | [CA2007: Do not directly await a Task](ca2007.md) | An asynchronous method [awaits](../../../csharp/language-reference/operators/await.md) a directly. When an asynchronous method awaits a directly, continuation occurs in the same thread that created the task. This behavior can be costly in terms of performance and can result in a deadlock on the UI thread. Consider calling to signal your intention for continuation. | diff --git a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md index 6ca8119122177..eccec5158faea 100644 --- a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md +++ b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md @@ -66,3 +66,4 @@ Performance rules support high-performance libraries and applications. | [CA1853: Unnecessary call to 'Dictionary.ContainsKey(key)'](ca1853.md) | There's no need to guard `Dictionary.Remove(key)` with `Dictionary.ContainsKey(key)`. already checks whether the key exists and doesn't throw if it doesn't exist. | | [CA1854: Prefer the 'IDictionary.TryGetValue(TKey, out TValue)' method](ca1854.md) | Prefer 'TryGetValue' over a Dictionary indexer access guarded by a 'ContainsKey' check. 'ContainsKey' and the indexer both look up the key, so using 'TryGetValue' avoids the extra lookup. | | [CA1855: Use Span\.Clear() instead of Span\.Fill()](ca1855.md) | It's more efficient to call than to call to fill the elements of the span with a default value. | +> | [CA1858: Use StartsWith instead of IndexOf](ca1855.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | diff --git a/docs/fundamentals/toc.yml b/docs/fundamentals/toc.yml index ab2f5d5a5348b..bfacfb85dce88 100644 --- a/docs/fundamentals/toc.yml +++ b/docs/fundamentals/toc.yml @@ -1177,6 +1177,8 @@ items: href: code-analysis/quality-rules/ca1854.md - name: CA1855 href: code-analysis/quality-rules/ca1855.md + - name: CA1858 + href: code-analysis/quality-rules/ca1858.md - name: SingleFile rules items: - name: Overview From d6defc66e6c71e0d8b34e1400d27a54c15e35290 Mon Sep 17 00:00:00 2001 From: Youssef1313 Date: Tue, 20 Dec 2022 20:32:35 +0200 Subject: [PATCH 2/4] Minor update --- docs/fundamentals/code-analysis/quality-rules/ca1858.md | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/docs/fundamentals/code-analysis/quality-rules/ca1858.md b/docs/fundamentals/code-analysis/quality-rules/ca1858.md index 8c52497c8a520..665d40f902e1a 100644 --- a/docs/fundamentals/code-analysis/quality-rules/ca1858.md +++ b/docs/fundamentals/code-analysis/quality-rules/ca1858.md @@ -27,7 +27,9 @@ dev_langs: ## Rule description -It's more efficient and clearer to call than to call and compare the result with zero to determine whether a string starts with a given prefix.. +It's more efficient and clearer to call than to call and compare the result with zero to determine whether a string starts with a given prefix. + +Using `IndexOf` will search the entire string, while using `StartsWith` will only compare at the beginning. ## How to fix violations From 4769f85720da9c597f6c92e9d95293ea2bfa7536 Mon Sep 17 00:00:00 2001 From: Youssef Victor Date: Tue, 20 Dec 2022 21:16:03 +0200 Subject: [PATCH 3/4] Apply suggestions from code review Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com> --- docs/fundamentals/code-analysis/quality-rules/ca1858.md | 2 +- docs/fundamentals/code-analysis/quality-rules/index.md | 2 +- .../code-analysis/quality-rules/performance-warnings.md | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/docs/fundamentals/code-analysis/quality-rules/ca1858.md b/docs/fundamentals/code-analysis/quality-rules/ca1858.md index 665d40f902e1a..f185dabb0b352 100644 --- a/docs/fundamentals/code-analysis/quality-rules/ca1858.md +++ b/docs/fundamentals/code-analysis/quality-rules/ca1858.md @@ -29,7 +29,7 @@ dev_langs: It's more efficient and clearer to call than to call and compare the result with zero to determine whether a string starts with a given prefix. -Using `IndexOf` will search the entire string, while using `StartsWith` will only compare at the beginning. +`IndexOf` searches the entire string, while `StartsWith` only compares at the beginning of the string. ## How to fix violations diff --git a/docs/fundamentals/code-analysis/quality-rules/index.md b/docs/fundamentals/code-analysis/quality-rules/index.md index 948544084ab0c..2bec8d86fbda1 100644 --- a/docs/fundamentals/code-analysis/quality-rules/index.md +++ b/docs/fundamentals/code-analysis/quality-rules/index.md @@ -151,7 +151,7 @@ The following table lists code quality analysis rules. > | [CA1853: Unnecessary call to 'Dictionary.ContainsKey(key)'](ca1853.md) | There's no need to guard `Dictionary.Remove(key)` with `Dictionary.ContainsKey(key)`. already checks whether the key exists and doesn't throw if it doesn't exist. | > | [CA1854: Prefer the 'IDictionary.TryGetValue(TKey, out TValue)' method](ca1854.md) | Prefer 'TryGetValue' over a Dictionary indexer access guarded by a 'ContainsKey' check. 'ContainsKey' and the indexer both look up the key, so using 'TryGetValue' avoids the extra lookup. | > | [CA1855: Use Span\.Clear() instead of Span\.Fill()](ca1855.md) | It's more efficient to call than to call to fill the elements of the span with a default value. | -> | [CA1858: Use StartsWith instead of IndexOf](ca1855.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | +> | [CA1858: Use StartsWith instead of IndexOf](ca1858.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | > | [CA2000: Dispose objects before losing scope](ca2000.md) | Because an exceptional event might occur that will prevent the finalizer of an object from running, the object should be explicitly disposed before all references to it are out of scope. | > | [CA2002: Do not lock on objects with weak identity](ca2002.md) |An object is said to have a weak identity when it can be directly accessed across application domain boundaries. A thread that tries to acquire a lock on an object that has a weak identity can be blocked by a second thread in a different application domain that has a lock on the same object. | > | [CA2007: Do not directly await a Task](ca2007.md) | An asynchronous method [awaits](../../../csharp/language-reference/operators/await.md) a directly. When an asynchronous method awaits a directly, continuation occurs in the same thread that created the task. This behavior can be costly in terms of performance and can result in a deadlock on the UI thread. Consider calling to signal your intention for continuation. | diff --git a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md index eccec5158faea..d2e3c136c1512 100644 --- a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md +++ b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md @@ -66,4 +66,4 @@ Performance rules support high-performance libraries and applications. | [CA1853: Unnecessary call to 'Dictionary.ContainsKey(key)'](ca1853.md) | There's no need to guard `Dictionary.Remove(key)` with `Dictionary.ContainsKey(key)`. already checks whether the key exists and doesn't throw if it doesn't exist. | | [CA1854: Prefer the 'IDictionary.TryGetValue(TKey, out TValue)' method](ca1854.md) | Prefer 'TryGetValue' over a Dictionary indexer access guarded by a 'ContainsKey' check. 'ContainsKey' and the indexer both look up the key, so using 'TryGetValue' avoids the extra lookup. | | [CA1855: Use Span\.Clear() instead of Span\.Fill()](ca1855.md) | It's more efficient to call than to call to fill the elements of the span with a default value. | -> | [CA1858: Use StartsWith instead of IndexOf](ca1855.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | +> | [CA1858: Use StartsWith instead of IndexOf](ca1858.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | From 35e704a561ff5d67874898dfd695d90a3d7fb0f0 Mon Sep 17 00:00:00 2001 From: Youssef Victor Date: Tue, 20 Dec 2022 21:16:22 +0200 Subject: [PATCH 4/4] Update docs/fundamentals/code-analysis/quality-rules/performance-warnings.md --- .../code-analysis/quality-rules/performance-warnings.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md index d2e3c136c1512..2f6f878bfd3a1 100644 --- a/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md +++ b/docs/fundamentals/code-analysis/quality-rules/performance-warnings.md @@ -66,4 +66,4 @@ Performance rules support high-performance libraries and applications. | [CA1853: Unnecessary call to 'Dictionary.ContainsKey(key)'](ca1853.md) | There's no need to guard `Dictionary.Remove(key)` with `Dictionary.ContainsKey(key)`. already checks whether the key exists and doesn't throw if it doesn't exist. | | [CA1854: Prefer the 'IDictionary.TryGetValue(TKey, out TValue)' method](ca1854.md) | Prefer 'TryGetValue' over a Dictionary indexer access guarded by a 'ContainsKey' check. 'ContainsKey' and the indexer both look up the key, so using 'TryGetValue' avoids the extra lookup. | | [CA1855: Use Span\.Clear() instead of Span\.Fill()](ca1855.md) | It's more efficient to call than to call to fill the elements of the span with a default value. | -> | [CA1858: Use StartsWith instead of IndexOf](ca1858.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. | +| [CA1858: Use StartsWith instead of IndexOf](ca1858.md) | It's more efficient to call than to call to check whether a string starts with a given prefix. |