Well, if Java can do it, so can I! Why not make my own C# string class that can do whatever I want it to do? Requirements? Here they are:
- I want it to work just like regular strings
- I want to know if the string is empty just by using it as an if clause, just like Javascript: if (text) doSomething(text);
- I want to see if it's a number just by adding a plus sign in front of it: var number = +text;
- I want to easily know if the string is null or whitespace!
OK, so first I want to get all the functionality of a normal string. So I will just inherit from it! Only I can't.
String is a sealed class in .Net.
Yet there is an abstract class that seems destined to be used by this:
ValueType! It's only implemented by all value types (more or less)
except String, but I will be the next guy to use it! Only I can't. If I try, I get the occult message: "Error CS0644 'EString' cannot derive from special class 'ValueType'". But it does help with something, if I try to inherit from it, it tells me what methods to implement:
Equals, GetHashCode and ToString.
OK, then, I will just do everything from scratch!
Start with a struct (no need for a class) that wraps a string _value field, then overwrite the equality methods:
public struct EString
{
private string _value;
public override bool Equals(object obj)
{
return String.Equals(obj, _value);
}
public override int GetHashCode()
{
return _value == null ? 0 : _value.GetHashCode();
}
public override string ToString()
{
return _value;
}
}
I used 0 for the hash code when the value is null because that's what the .Net object
GetHashCode() does. Now, in order for this to work as a string, I need some
implicit conversion from string to my EString class. So add these two beauties:
public string Value { get => _value; }
private EString(string value) { _value = value; }
public static implicit operator string(EString estring)
{
return estring.Value;
}
public static implicit operator EString(string value)
{
return new EString(value);
}
EString now supports stuff like
EString text="Something";, but I want more! Let's
overload some operators. I want to be able to see if a string is null or empty just like in Javascript:
public static bool operator !(EString estring)
{
return String.IsNullOrEmpty(estring);
}
public static bool operator true(EString estring)
{
return !!estring;
}
public static bool operator false(EString estring)
{
return !estring;
}
Yes, ladies and gentlemen,
true and false are not only boolean constants, but also operators. That doesn't mean something like this is legal:
if (text==true) ..., but you can use stuff like
if (text) ... or
text ? "something" : "empty". Overloading the ! operator allows also something more useful like
if (!text) [this shit is empty].
Moar! How about a simple way to know if the string is null or empty or whitespace? Let's overload the ~ operator. How about getting the number encoded into the text? Let's overload the + operator. Here is the final result:
public struct EString
{
private string _value;
public string Value { get => _value; }
private EString(string value) { _value = value; }
public override bool Equals(object obj)
{
return String.Equals(obj, _value);
}
public override int GetHashCode()
{
return _value == null ? 0 : _value.GetHashCode();
}
public override string ToString()
{
return _value;
}
public static bool operator !(EString estring)
{
return String.IsNullOrEmpty(estring);
}
public static bool operator true(EString estring)
{
return !!estring;
}
public static bool operator false(EString estring)
{
return !estring;
}
public static bool operator ~(EString estring)
{
return String.IsNullOrWhiteSpace(estring);
}
public static decimal operator +(EString estring)
{
return decimal.TryParse(estring.Value, out decimal d) ? d : decimal.Zero;
}
public static implicit operator string(EString estring)
{
return estring.Value;
}
public static implicit operator EString(string value)
{
return new EString(value);
}
}
Disclamer: I did this mostly for fun. I can't condone replacing your strings with my class, but look at these examples for usage:
EString s=inputText;
if (!~s) {
var d = Math.Round(+s,2);
if (d != 0) {
Console.WriteLine("Number was introduced: "+d);
}
}
Caveat lector: while this works, meaning it compiles and runs, you might have problems when you are trying to package your work into npm packages. When ng-packagr is used with such a system (often found in older versions of Angular as index.ts files) it throws a really unhelpful exception: TypeError: Cannot read property 'module' of undefined somewhere in bundler.js. The bug is being tracked here, but it doesn't seem to be much desire to address it. Apparently, I have rediscovered the concept of barrel, which now seems to have been abandoned and even completely expunged from Angular docs.