Update "How to: Modify string" #4519

BillWagner · 2018-02-28T19:32:41Z

The following updates are part of this PR:

Update the samples to use modern C#.
Add all sample code to a single downloadable project.
Leverage the C# interactive REPL
Highlight the immutability of strings in every example.

pkulikov · 2018-03-02T18:50:56Z

.openpublishing.redirection.json

+        },
+        {    
+            "source_path": "docs/csharp/programming-guide/strings/how-to-modify-string-contents.md",
+            "redirect_url": "/dotnet/standard/base-types/modify-string-contents"


redirect_url should be /dotnet/csharp/how-to/modify-string-contents?

pkulikov · 2018-03-02T18:58:35Z

docs/csharp/how-to/modify-string-contents.md

+
+# How to: Modify String Contents (C# Programming Guide)
+
+You can't modify the contents of a string after it has been created. The <xref:System.String?displayProperty=nameWithType> class is *immutable*. The examples in this article show how to create a new string object that represents the result of some change to an existing string.


But the last section of this article shows how to modify string-in-place, so the first sentence doesn't sound convincing. I don't know how to say that not unsafe strings are immutable, which means that any string modification creates a new string rather than updating the given string. What if we talk not about modifying strings, but transforming (but then too much changes through docs...)?

I did make a few updates here based on your comment.

First, I added "typically" to the first sentence. I tried introducing the term "unsafe code" there, but I rejected it because the article is not really about using unsafe code, but about how to change the value of strings.

I want to continue to use the term "Modifying strings" because that is a more common search term than "transforming". I agree it is a bit inaccurate, and the content of the article works to make that clear.

Next, I added a bit more explanatory text in the paragraph that introduces the unsafe sample.

I hope that adds the clarity we need.

pkulikov · 2018-03-02T19:00:16Z

docs/csharp/how-to/modify-string-contents.md

+
+## Trim whitespace
+
+You can use the <xref:System.String.Trim%2A?displayProperty=nameWithType>, <xref:System.String.TrimStart%2A?displayProperty=nameWithType>, and <xref:System.String.TrimEnd%2A?displayProperty=nameWithType> methods removes any leading or trailing whitespace.  The following code shows an example of each. The source string does not change; these methods return a new string with the modified contents.


After the method list should be ...methods to remove...

pkulikov · 2018-03-02T19:06:10Z

docs/csharp/how-to/modify-string-contents.md

+
+The following example is provided for those rare situations where you want to modify a string in-place by using unsafe code. The example shows how to access the individual characters "in-place" by using the fixed keyword. It also demonstrates one possible side effect of unsafe operations on strings that results from the way that the C# compiler stores (interns) strings internally. In general, you shouldn't use this technique unless it is absolutely necessary.
+
+[!code-csharp-interactive[unsafe ways to create a new string](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#7)]  


Like in other How-Tos on strings, let's insert paragraph about where to find the code used in snippets. Then zip-file should be updated?

Thanks for the reminder. I wanted to wait until we'd merged the How to search strings PR.

pkulikov · 2018-03-02T19:13:40Z

docs/csharp/programming-guide/strings/index.md

@@ -118,7 +118,7 @@ string s = String.Empty;

 |Topic|Description|  
 |-----------|-----------------|  
-|[How to: Modify String Contents](../../../csharp/programming-guide/strings/how-to-modify-string-contents.md)|Provides a code example that illustrates how to modify the contents of strings.|  
+|[How to: Modify String Contents](../../how-to/modify-string-contents.md)|Provides a code example that illustrates how to modify the contents of strings.|  


Instead of Provides a code example... it better sounds like in a row below on concatenation: Illustrates... Not for this PR: description of How to: Parse Strings... also might be updated.
Though, description of concatenation is not correct too: string methods are also used for concatenation. I'd review that table as a whole.

pkulikov · 2018-03-02T19:19:10Z

samples/snippets/csharp/how-to/strings/ModifyStrings.cs

+                System.Text.RegularExpressions.RegexOptions.IgnoreCase);
+            Console.WriteLine(source);
+
+            string localReplaceMatchCase(System.Text.RegularExpressions.Match matchExpression)


Shouldn't local methods start with capital letter as well?
Anyway, a good example of local method usage.

rpetrusha

I've left a number of comments, @BillWagner. The REPL really makes a difference here, and the pointer example is simple and extremely effective.

rpetrusha · 2018-03-06T23:38:26Z

docs/csharp/how-to/modify-string-contents.md

+
+# How to: Modify String Contents (C# Programming Guide)
+
+You can't easily modify the contents of a string after it has been created. The <xref:System.String?displayProperty=nameWithType> class is *immutable*. The examples in this article show how to create a new string object that represents the result of some change to an existing string.


This doesn't seem like a good starting point or good phrasing, especially if this is intended as an introductory topic. It sort of reads, "Title: How to modify strings; Answer: You can't". (Actually, you can't easily is completely incorrect.) In some sense immutablity is an implementation detail. (The primitives, for example, are also immutable, though they appear not to be.) Operationally, this simply means you have to assign the changed string to a new string or nothing is changed (a common error with some string methods), which is where I would start with the explanation. I'd only mention that this is immutable afterwards.

This was a great suggestion that helped drive the tone better. Thanks! I re-wrote the opening and moved the discussion of immutable to the last section.

rpetrusha · 2018-03-06T23:42:27Z

docs/csharp/how-to/modify-string-contents.md

+
+[!code-csharp-interactive[replace creates a new string](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#1)]  
+
+You can see in the preceding example that the original string, `source`, is not modified. The <xref:System.String.Replace%2A?displayProperty=nameWithType> creates a new `string` containing the modifications.


creates --> method creates (or else delete "The" at the beginning of the sentence)

rpetrusha · 2018-03-06T23:44:09Z

docs/csharp/how-to/modify-string-contents.md

+
+The <xref:System.String.Replace%2A> method can replace either strings or single characters. In both cases, every occurrence of the sought text is replaced.  The following example replaces all ' ' characters with '_':
+
+[!code-csharp-interactive[replace characters](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#2)]  


I think that it might be useful to include output at the end of each example even if it's runnable, for those who don't want to run it.

I advocate not to include output as it makes code snippets take more space (my comment as a reader) and harder to maintain (as a contributor). One more thing: when I run and change code, output comment becomes wrong and just takes space between code and actual output (my comment as a user).

😆 This mirrors the split feedback I've gotten when I've shown pages at conferences. I created #4571 to see which people like. Let's see what responses we get. For now, I left the comments in place here.

rpetrusha · 2018-03-06T23:44:51Z

docs/csharp/how-to/modify-string-contents.md

+
+The source string is unchanged, and a new string is returned with the replacement.
+
+## Trim whitespace


white space as a noun should be 2 words ("white space")

rpetrusha · 2018-03-06T23:47:39Z

docs/csharp/how-to/modify-string-contents.md

+
+## Replace patterns
+
+You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace patterns with new patterns. The following example makes use of the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace%2A?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. That function uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.


you don't replace patterns with patterns; you identify text that conforms to a pattern, which you replace with text that is defined by a pattern.
makes use of --> uses
<xref:System.Text.RegularExpressions.Regex.Replace%2A?displayProperty=nameWithType> should be a link to the overload used or make it clear that this is a subset of replace methods, since not all have a MatchEvaluator argument.
Mention the name of the function that provides the logic of the replacement -- LocalReplaceMatchCase -- to make it clear that it's your function, and not Regex.Replace, that provides the StringBuilder functionality. In terms of the code, since you're using a local function, I think I'd be inclined to include the entire source, or at least all of the Main method, for anyone who might not be aware of local functions.

I updated everything in this comment, except expanding the sample to include the example method. If I did that, it doesn't run in the REPL.

rpetrusha · 2018-03-06T23:58:44Z

docs/csharp/how-to/modify-string-contents.md

+
+You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace patterns with new patterns. The following example makes use of the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace%2A?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. That function uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.
+
+The search pattern, "the\s" searches for the word "the" followed by a whitespace character. That part of the pattern ensures that it doesn't match "there" in the source string. Regular expressions are most useful for searching and replacing text that follows a pattern, rather than known text. See [How to: search strings](search-strings.md) for more details.


whitespace --> white-space
the sentence "Regular expressions are most useful..." should go earlier. You might also link to the regular expression replacement language elements -- people have a lot of difficulty with the regex replace method.

rpetrusha · 2018-03-07T00:05:59Z

docs/csharp/how-to/modify-string-contents.md

+## Unsafe modifications to string
+
+Using **unsafe** code, you can modify a string "in place" after it has been created. Unsafe code bypasses many of the features of .NET designed to minimize certain types of bugs in code. 
+The following example is provided for those rare situations where you want to modify a string in-place using unsafe code. The example shows how to access the individual characters "in-place" by using the fixed keyword. It also demonstrates one possible side effect of unsafe operations on strings that results from the way that the C# compiler stores (interns) strings internally. In general, you shouldn't use this technique unless it is absolutely necessary.


I'd be somewhat more precise here. Fixed doesn't permit access, it just prevents GC from moving the object you might want to access.

rpetrusha · 2018-03-07T00:06:20Z

docs/csharp/how-to/modify-string-contents.md

+
+## Unsafe modifications to string
+
+Using **unsafe** code, you can modify a string "in place" after it has been created. Unsafe code bypasses many of the features of .NET designed to minimize certain types of bugs in code. 


Links to unsafe, fixed, etc., would also be good here.

What about the link to how strings are stored (intern)? Or that would be too many implementation details?

Added links for fixed and unsafe. I didn't find a good topic on interned strings though.

rpetrusha · 2018-03-07T00:07:42Z

docs/csharp/how-to/modify-string-contents.md

+Using **unsafe** code, you can modify a string "in place" after it has been created. Unsafe code bypasses many of the features of .NET designed to minimize certain types of bugs in code. 
+The following example is provided for those rare situations where you want to modify a string in-place using unsafe code. The example shows how to access the individual characters "in-place" by using the fixed keyword. It also demonstrates one possible side effect of unsafe operations on strings that results from the way that the C# compiler stores (interns) strings internally. In general, you shouldn't use this technique unless it is absolutely necessary.
+
+[!code-csharp-interactive[unsafe ways to create a new string](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#7)]  


Nice example!

That was already there. Was it originally yours? 👏

Switching tasks.

I want to see if I can use local functions in C# interactive.

Ready for my first review.

rpetrusha

I've left a number of minor comments, @BillWagner, but this looks really good overall. You can merge once you decide which ones you want to address.

rpetrusha · 2018-03-08T23:47:09Z

docs/csharp/how-to/modify-string-contents.md

+
+# How to: Modify String Contents (C# Programming Guide)
+
+This article demonstrates several techniques to produce a `string` by modifying an existing `string`. All the techniques demonstrated return the result of the modifications as a `string` object. To clearly demonstrate this, the examples all store the result in a new variable. You can then examine both the original `string` and the `string` resulting from the modification when you run each example. 


This is a much better opening paragraph, Bill! I'd modify the second sentence just a bit to stress that a new string is returned -- "as a new `string` object."

rpetrusha · 2018-03-08T23:49:04Z

docs/csharp/how-to/modify-string-contents.md

+
+This article demonstrates several techniques to produce a `string` by modifying an existing `string`. All the techniques demonstrated return the result of the modifications as a `string` object. To clearly demonstrate this, the examples all store the result in a new variable. You can then examine both the original `string` and the `string` resulting from the modification when you run each example. 
+
+There are several techniques demonstrated in this article. You can replace existing text. Other methods search for patterns and replace matching text with other text. You can also treat a string as a sequence of characters. You can also use convenience methods that remove whitespace. YOu should choose the techniques that most closely matches your scenario.


Rather than "Other methods", "You" to maintain parallelism
No "also" in "You can also treat"
whitespace --> white space (2 words)
YOu has a typo --> You
matches ---> match

rpetrusha · 2018-03-08T23:49:42Z

docs/csharp/how-to/modify-string-contents.md

+
+## Replace text
+
+The following code demonstrates this *immutable* property of strings. It creates a new string by replacing existing text with a substitute.


I'd move this first sentence to after the code example.

That does flow much better.

rpetrusha · 2018-03-08T23:52:08Z

docs/csharp/how-to/modify-string-contents.md

+
+[!code-csharp-interactive[replace characters](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#2)]  
+
+The source string is unchanged, and a new string is returned with the replacement.


I'm not sure why everything from the code label on is italicized. Is '_' interpreted as *?

I think it's the _. The italics does not show up on the review site.

rpetrusha · 2018-03-08T23:52:33Z

docs/csharp/how-to/modify-string-contents.md

+
+## Trim white space
+
+You can use the <xref:System.String.Trim%2A?displayProperty=nameWithType>, <xref:System.String.TrimStart%2A?displayProperty=nameWithType>, and <xref:System.String.TrimEnd%2A?displayProperty=nameWithType> methods to remove any leading or trailing whitespace.  The following code shows an example of each. The source string does not change; these methods return a new string with the modified contents.


whitespace --> white space

I did a global search for whitespace.

rpetrusha · 2018-03-08T23:54:46Z

docs/csharp/how-to/modify-string-contents.md

+
+## Replace matching patterns
+
+You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace text matching patterns with new text, possibly defined by a pattern. The following example uses the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace(System.String,System.String,System.Text.RegularExpressions.MatchEvaluator,System.Text.RegularExpressions.RegexOptions)?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. In this example, that function, `LocalReplaceMatchCase` is a **local function**, declared inside the sample method. `LocalReplaceMatchCase` uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.


no comma after "local function"

rpetrusha · 2018-03-08T23:56:02Z

docs/csharp/how-to/modify-string-contents.md

+
+You can produce a character array from a string, modify the contents of the array, and then create a new string from the modified contents of the array. 
+
+The following example shows how to replace a set of characters in a string. First, it uses the <xref:System.String.ToCharArray?displayProperty=nameWithName> method to create an array of characters. Then, it uses the <xref:System.String.IndexOf%2A> method to find the starting index of the word "fox." Then, the next three characters are replaced with a different word. Finally, a new string is constructed from the updated character array.


No comma after the two occurrences of "Then"

rpetrusha · 2018-03-08T23:59:30Z

docs/csharp/how-to/modify-string-contents.md

+## Unsafe modifications to string
+
+Using **unsafe** code, you can modify a string "in place" after it has been created. Unsafe code bypasses many of the features of .NET designed to minimize certain types of bugs in code. You need to use unsafe code to modify a string in place because the string class is designed as an **immutable** type. Once it has been created, its value does not change. Unsafe code circumvents this property by accessing and modifying the memory used by a `string` without using normal `string` methods.
+The following example is provided for those rare situations where you want to modify a string in-place using unsafe code. The example shows how to use the `fixed` keyword. The `fixed` keyword prevents the garbage collector (GC) from moving the string object in memory while code accesses the memory using the unsafe pointer. It also demonstrates one possible side effect of unsafe operations on strings that results from the way that the C# compiler stores (interns) strings internally. In general, you shouldn't use this technique unless it is absolutely necessary. You can learn more in the articles on [unsafe](../langauge-reference/keywords/unsafe.md) and [fixed](../language-reference/keywords/fixed.md).


It might be useful to link to some information on interning strings: ([interns](<xref:System.String.Intern%2A>))

Good suggestion. I looked and could not find a good topi in our conceptual docs.

@BillWagner

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BillWagner requested a review from rpetrusha March 2, 2018 02:39

BillWagner changed the title ~~[WIP] Update "How to: Modify string"~~ Update "How to: Modify string" Mar 2, 2018

BillWagner requested a review from mairaw March 2, 2018 16:03

pkulikov reviewed Mar 2, 2018

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rpetrusha suggested changes Mar 7, 2018

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		# How to: Modify String Contents (C# Programming Guide)

		You can't modify the contents of a string after it has been created. The <xref:System.String?displayProperty=nameWithType> class is immutable. The examples in this article show how to create a new string object that represents the result of some change to an existing string.


		## Trim whitespace

		You can use the <xref:System.String.Trim%2A?displayProperty=nameWithType>, <xref:System.String.TrimStart%2A?displayProperty=nameWithType>, and <xref:System.String.TrimEnd%2A?displayProperty=nameWithType> methods removes any leading or trailing whitespace. The following code shows an example of each. The source string does not change; these methods return a new string with the modified contents.


		The following example is provided for those rare situations where you want to modify a string in-place by using unsafe code. The example shows how to access the individual characters "in-place" by using the fixed keyword. It also demonstrates one possible side effect of unsafe operations on strings that results from the way that the C# compiler stores (interns) strings internally. In general, you shouldn't use this technique unless it is absolutely necessary.

		[!code-csharp-interactive[unsafe ways to create a new string](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#7)]


		# How to: Modify String Contents (C# Programming Guide)

		You can't easily modify the contents of a string after it has been created. The <xref:System.String?displayProperty=nameWithType> class is immutable. The examples in this article show how to create a new string object that represents the result of some change to an existing string.


		[!code-csharp-interactive[replace creates a new string](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#1)]

		You can see in the preceding example that the original string, `source`, is not modified. The <xref:System.String.Replace%2A?displayProperty=nameWithType> creates a new `string` containing the modifications.


		The <xref:System.String.Replace%2A> method can replace either strings or single characters. In both cases, every occurrence of the sought text is replaced. The following example replaces all ' ' characters with '_':

		[!code-csharp-interactive[replace characters](../../../samples/snippets/csharp/how-to/strings/ModifyStrings.cs#2)]


		The source string is unchanged, and a new string is returned with the replacement.

		## Trim whitespace


		## Replace patterns

		You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace patterns with new patterns. The following example makes use of the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace%2A?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. That function uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.


		You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace patterns with new patterns. The following example makes use of the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace%2A?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. That function uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.

		The search pattern, "the\s" searches for the word "the" followed by a whitespace character. That part of the pattern ensures that it doesn't match "there" in the source string. Regular expressions are most useful for searching and replacing text that follows a pattern, rather than known text. See [How to: search strings](search-strings.md) for more details.


		## Unsafe modifications to string

		Using unsafe code, you can modify a string "in place" after it has been created. Unsafe code bypasses many of the features of .NET designed to minimize certain types of bugs in code.


		# How to: Modify String Contents (C# Programming Guide)

		This article demonstrates several techniques to produce a `string` by modifying an existing `string`. All the techniques demonstrated return the result of the modifications as a `string` object. To clearly demonstrate this, the examples all store the result in a new variable. You can then examine both the original `string` and the `string` resulting from the modification when you run each example.


		This article demonstrates several techniques to produce a `string` by modifying an existing `string`. All the techniques demonstrated return the result of the modifications as a `string` object. To clearly demonstrate this, the examples all store the result in a new variable. You can then examine both the original `string` and the `string` resulting from the modification when you run each example.

		There are several techniques demonstrated in this article. You can replace existing text. Other methods search for patterns and replace matching text with other text. You can also treat a string as a sequence of characters. You can also use convenience methods that remove whitespace. YOu should choose the techniques that most closely matches your scenario.


		## Replace text

		The following code demonstrates this immutable property of strings. It creates a new string by replacing existing text with a substitute.


		## Trim white space

		You can use the <xref:System.String.Trim%2A?displayProperty=nameWithType>, <xref:System.String.TrimStart%2A?displayProperty=nameWithType>, and <xref:System.String.TrimEnd%2A?displayProperty=nameWithType> methods to remove any leading or trailing whitespace. The following code shows an example of each. The source string does not change; these methods return a new string with the modified contents.


		## Replace matching patterns

		You can use [regular expressions](../../standard/base-types/regular-expressions.md) to replace text matching patterns with new text, possibly defined by a pattern. The following example uses the <xref:System.Text.RegularExpressions.Regex?displayProperty=nameWithType> class to find a pattern in a source string and replace it with proper capitalization. The <xref:System.Text.RegularExpressions.Regex.Replace(System.String,System.String,System.Text.RegularExpressions.MatchEvaluator,System.Text.RegularExpressions.RegexOptions)?displayProperty=nameWithType> method takes a function that provides the logic of the replacement as one of its arguments. In this example, that function, `LocalReplaceMatchCase` is a local function, declared inside the sample method. `LocalReplaceMatchCase` uses the <xref:System.Text.StringBuilder?displayProperty=nameWithType> class to build the replacement string with proper capitalization.


		You can produce a character array from a string, modify the contents of the array, and then create a new string from the modified contents of the array.

		The following example shows how to replace a set of characters in a string. First, it uses the <xref:System.String.ToCharArray?displayProperty=nameWithName> method to create an array of characters. Then, it uses the <xref:System.String.IndexOf%2A> method to find the starting index of the word "fox." Then, the next three characters are replaced with a different word. Finally, a new string is constructed from the updated character array.

Update "How to: Modify string" #4519

Update "How to: Modify string" #4519

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