Rob’s Tech Blog

I don’t think I’ve seen a single project without some form of string parsing: int.Parse(txtName.Text), anyone?.

Here’s a cool way to take a string and parse it to whatever you want, enum, double, bool, it works on anything that’s both IConvertible and a struct (ok I lied about “anything”). It’s an extension method, but could just be a library call if that pleases you (or your compiler) more.

 

public static T? As<T>(this string s) where T : struct, IConvertible
{
    try
    {
        Type type = typeof(T);
        bool isEnum = typeof(Enum).IsAssignableFrom(type);
        return (T)(isEnum
            ? Enum.Parse(type, s, true)
            : Convert.ChangeType(s, type));
    }
    catch
    {
        return null;
    }
}

Note that it just returns null if the parse fails – this actually ends up being really simple to use:

• If you KNOW the parse shouldn’t fail, you just call .Value – which will give you an exception if the parse somehow did fail (this is a good thing)
• If you want to see if the parse failed, you can check the .HasValue property
• If you want to provide a fallback value, you can just use the ?? operator

---

Here are the TDD tests for the code, to give you idea of how flexible this is:

[TestMethod]
public void StringAsInt()
{
    Assert.AreEqual(5, "5".As<int>());
    Assert.AreEqual(25, "25".As<int>());
    Assert.AreEqual(null, "foobar".As<int>());
}

[TestMethod]
public void StringAsDouble()
{
    Assert.AreEqual(5.5, "5.5".As<double>());
    Assert.AreEqual(-25.2, "-25.2".As<double>());
    Assert.AreEqual(null, "foobar".As<double>());
}

[TestMethod]
public void StringAsBool()
{
    Assert.AreEqual(true, "true".As<bool>());
    Assert.AreEqual(false, "false".As<bool>());
    Assert.AreEqual(null, "foobar".As<bool>());
}

[TestMethod]
public void StringParseEnum()
{
    Assert.AreEqual(ContactPreference.Email, "Email".As<ContactPreference>());
    Assert.AreEqual(null, "Schmemail".As<ContactPreference>());
    Assert.AreEqual(null, ((string)null).As<ContactPreference>());
    Assert.AreEqual(ContactPreference.MobilePhone, "MobilePhone".As<ContactPreference>());
}
enum ContactPreference
{
    Email,
    MobilePhone
}

Enjoy! – Rob