Gotcha: no prefix increment/decrement VB.net operators, but get parsed

In C/C++ and C# one has useful prefix (++index) and postfix (index++) increment operators and corresponding decrement ones.

Although they have a single operant, they’re not working like functions as single + or – prefix would do, but instead they cause side-effects – they edit the variable passed to them. The prefix increment operator first increases a variable’s value, then returns it as result, while the postfix one first returns a variable’s value, then increases it.

Visual Basic.net doesn’t have such operators (and they don’t seem to plan to add such from their response on related feedback at Microsoft Connect.

However, if you type-in

Dim x = ++y

the compiler won’t complain. In fact, it won’t complain even if you type

Dim x = +++++y

The reason is because it thinks this last crazy-looking expression is:

Dim x = +(+(+(+(+y))))

Similarly, it accepts expressions like

Dim x = –y

and

Dim x = —–y

So a programmer coming from C# or converting C# code to VB.net has to be extra careful when converting ++index expressions to use their own implementation as a function that takes a ByRef parameter

.NET String extension methods to check for array of prefixes or suffixes

Seems StartsWith and EndsWith methods of String class in .NET are missing a version that accepts multiple (as an array) prefixes or suffixes respectively when testing the string. To achieve this I just added the following extension methods to StringExtensions class (of Utils.Extensions namespace) under Utils.Silverlight project at the ClipFlair source code.

public static bool StartsWith(
  this string s, 
  string[] suffixes, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  foreach (string suffix in suffixes)
    if (s.StartsWith(suffix, comparisonType))
      return true;
  return false;
}

public static bool EndsWith(
  this string s, 
  string[] suffixes, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  foreach (string suffix in suffixes)
    if (s.EndsWith(suffix, comparisonType)) 
      return true;
  return false;
}

 

To use them, you add a reference to Utils.Silverlight project to your own one and then add a using clause for the namespace that hosts a static class with these extension methods (e.g. “using Utils.Extensions;”) and then you can use them on any String at the respective source file. Can even use them on literal strings, since most .NET compilers support Boxing of literals into respective types.

I’m using a default value for the comparisonType method argument to make it optional. I use StringComparison.CurrentCulture as the default value for it (performing a word case-sensitive and culture-sensitive comparison using the current culture), as Microsoft is doing at “String.StartsWith(String)” method. However, do note the following text from that method’s documentation:

Notes to Callers

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To determine whether a string begins with a particular substring by using the string comparison rules of the current culture, call the StartsWith(String, StringComparison) method overload with a value of StringComparison.CurrentCulture for its comparisonType parameter.

.NET String class extensions to replace prefix or suffix

Just added the following extension methods to StringExtensions class (of Utils.Extensions namespace) under Utils.Silverlight project at the ClipFlair source code.

public static string ReplacePrefix(
  this string s,
  string fromPrefix, 
  string toPrefix, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  return (s.StartsWith(fromPrefix, comparisonType)) ? 
                         toPrefix + s.Substring(fromPrefix.Length) : s;
}

public static string ReplacePrefix(
  this string s, 
  string[] fromPrefix,
  string toPrefix, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  foreach (string prefix in fromPrefix)
    if (s.StartsWith(prefix, comparisonType))
      return toPrefix + s.Substring(prefix.Length);
  return s;
}

public static string ReplaceSuffix(
  this string s, 
  string fromSuffix, 
  string toSuffix, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  return (s.EndsWith(fromSuffix, comparisonType)) ? 
                   s.Substring(0, s.Length - fromSuffix.Length) + toSuffix : s;
}

public static string ReplaceSuffix(
  this string s,
  string[] fromSuffix, 
  string toSuffix, 
  StringComparison comparisonType = StringComparison.CurrentCulture)
{
  foreach (string suffix in fromSuffix)
    if (s.EndsWith(suffix, comparisonType))
      return s.Substring(0, s.Length - suffix.Length) + toSuffix;
  return s;
}

 

To use them, you add a reference to Utils.Silverlight project to your own one and then add a using clause for the namespace that hosts a static class with these extension methods (e.g. “using Utils.Extensions;”) and then you can use them on any String at the respective source file. Can even use them on literal strings, since most .NET compilers support Boxing of literals into respective types.

e.g.

s = s.ReplacePrefix("https://", "http://", StringComparison.OrdinalIgnoreCase);

//– converts https:// prefix to http:// ignoring character case

or

s = s.ReplacePrefix(new String[]{"https://", "http://"}, "", StringComparison.OrdinalIgnoreCase);

//– removes https:// or http:// prefix ignoring character case

 

Update:

I added a default value for the comparisonType method argument to make it optional. I use StringComparison.CurrentCulture as the default value for it (performing a word case-sensitive and culture-sensitive comparison using the current culture), as Microsoft is doing at “String.StartsWith(String)” method. However, do note the following text from that method’s documentation:

Notes to Callers

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To determine whether a string begins with a particular substring by using the string comparison rules of the current culture, call the StartsWith(String, StringComparison) method overload with a value of StringComparison.CurrentCulture for its comparisonType parameter.